The major difference between an open in a parallel circuit and an open in a series circuit is that in the parallel circuit the open would not necessarily disable the circuit. If the open condition occurs in a series portion of the circuit, there will be no current because there is no complete path for current flow. If, on the other hand, the open occurs in a parallel path, some current will still flow in the circuit. The parallel branch where the open occurs will be effectively disabled, total resistance of the circuit will INCREASE, and total current will DECREASE.
To clarify these points, figure 3-61 illustrates a series parallel circuit. First the effect of an open in the series portion of this circuit will be examined. Figure 3-61(A) shows the normal circuit, RT = 40 ohms and IT = 3 amps. In figure 3-61(B) an open is shown in the series portion of the circuit, there is no complete path for current and the resistance of the circuit is considered to be infinite.
In figure 3-61(C) an open is shown in the parallel branch of R 3. There is no path for current through R3. In the circuit, current flows through R1 and R2 only. Since there is only one path for current flow, R1 and R2 are effectively in series.
Under these conditions RT� ���� �DQG�,T = 1 amp. As you can see, when an open occurs in a parallel branch, total circuit resistance increases and total circuit current decreases.
A short circuit in a parallel network has an effect similar to a short in a series circuit. In general, the short will cause an increase in current and the possibility of component damage regardless of the type of
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circuit involved. To illustrate this point, figure 3-62 shows a series-parallel network in which shorts are developed. In figure 3-62 (A) the normal circuit is shown. RT = 40 ohms and IT = 3 amps.
In figure 3-62 (B), R1 has shorted. R1 now has zero ohms of resistance. The total of the resistance of the circuit is now equal to the resistance of the parallel network of R2 and R 3, or 20 ohms. Circuit current has increased to 6 amps. All of this current goes through the parallel network (R2, R 3) and this increase in current would most likely damage the components.
In figure 3-62 (C), R 3 has shorted. With R 3 shorted there is a short circuit in parallel with R2. The short circuit routes the current around R2, effectively removing R2 from the circuit. Total circuit resistance is now equal to the resistance of R1, or 20 ohms.
As you know, R2 and R 3 form a parallel network. Resistance of the network can be calculated as follows:
Given:
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Solution:
The total circuit current with R 3 shorted is 6 amps. All of this current flows through R1 and would most likely damage R1. Notice that even though only one portion of the parallel network was shorted, the entire paralleled network was disabled.
Opens and shorts alike, if occurring in a circuit, result in an overall change in the equivalent resistance. This can cause undesirable effects in other parts of the circuit due to the corresponding change in the total current flow. A short usually causes components to fail in a circuit which is not properly fused or otherwise protected. The failure may take the form of a burned-out resistor, damaged source, or a fire in the circuit components and wiring.
Fuses and other circuit protection devices are installed in equipment circuits to prevent damage caused by increases in current. These circuit protection devices are designed to open if current increases to a predetermined value. Circuit protection devices are connected in series with the circuit or portion of the circuit that the device is protecting. When the circuit protection device opens, current flow ceases in the circuit.
A more thorough explanation of fuses and other circuit protection devices is presented in Module 3, Introduction to Circuit Protection, Control, and Measurement.
Q46. What is the effect on total resistance and total current in a circuit if an open occurs in (a) a parallel branch, and (b) in a series portion?
Q47. What is the effect on total resistance and total current in a circuit if a short occurs in (a) a parallel branch, and (b) in a series portion?
Q48. If one branch of a parallel network is shorted, what portion of circuit current flows through the remaining branches?
Most electrical and electronics equipment use voltages of various levels throughout their circuitry.
One circuit may require a 90-volt supply, another a 150-volt supply, and still another a 180-volt supply. These voltage requirements could be supplied by three individual power sources. This method is expensive and requires a considerable amount of room. The most common method of supplying these voltages is to use a single voltage source and a VOLTAGE DIVIDER. Before voltage dividers are explained, a review of what was discussed earlier concerning voltage references may be of help.
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As you know, some circuits are designed to supply both positive and negative voltages. Perhaps now you wonder if a negative voltage has any less potential than a positive voltage. The answer is that 100 volts is 100 volts. Whether it is negative or positive does not affect the feeling you get when you are shocked.
Voltage polarities are considered as being positive or negative in respect to a reference point, usually ground. Figure 3-63 will help to illustrate this point.
Figure 3-63(A) shows a series circuit with a voltage source of 100 volts and four 50-ohm resistors connected in series. The ground, or reference point, is connected to one end of resistor R
1. The current in this circuit determined by Ohm’s law is .5 amp. Each resistor develops (drops) 25 volts. The five tap-off points indicated in the schematic are points at which the voltage can be measured. As indicated on the schematic, the voltage measured at each of the points from point A to point E starts at zero volts and becomes more positive in 25 volt steps to a value of positive 100 volts.
In figure 3-63(B), the ground, or reference point has been moved to point B. The current in the circuit is still .5 amp and each resistor still develops 25 volts. The total voltage developed in the circuit remains at 100 volts, but because the reference point has been changed, the voltage at point A is negative 25 volts. Point E, which was at positive 100 volts in figure 3-63(A), now has a voltage of positive 75 volts. As you can see the voltage at any point in the circuit is dependent on three factors; the current through the resistor, the ohmic value of the resistor, and the reference point in the circuit.
A typical voltage divider consists of two or more resistors connected in series across a source voltage (Es). The source voltage must be as high or higher than any voltage developed by the voltage divider. As the source voltage is dropped in successive steps through the series resistors, any desired
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portion of the source voltage may be "tapped off" to supply individual voltage requirements. The values of the series resistors used in the voltage divider are determined by the voltage and current requirements of the loads.
Figure 3-64 is used to illustrate the development of a simple voltage divider. The requirement for this voltage divider is to provide a voltage of 25 volts and a current of 910 milliamps to the load from a source voltage of 100 volts. Figure 3-64(A) provides a circuit in which 25 volts is available at point B. If the load was connected between point B and ground, you might think that the load would be supplied with 25 volts. This is not true since the load connected between point B and ground forms a parallel network of the load and resistor R1. (Remember that the value of resistance of a parallel network is always less than the value of the smallest resistor in the network.)
Since the resistance of the network would now be less than 25 ohms, the voltage at point B would be less than 25 volts. This would not satisfy the requirement of the load.
To determine the size of resistor used in the voltage divider, a rule-of-thumb is used. The current in the divider resistor should equal approximately 10 percent of the load current. This current, which does not flow through any of the load devices, is called bleeder current.
Given this information, the voltage divider can be designed using the following steps.
1. Determine the load requirement and the available voltage source.
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2. Select bleeder current by applying the 10% rule-of-thumb.
3. Calculate bleeder resistance.
The value of R1 may be rounded off to 275 ohms:
4. Calculate the total current (load plus bleeder).
5. Calculate the resistance of the other divider resistor(s).
The voltage divider circuit can now be drawn as shown in figure 3-64(B). Q49. What information must be known to determine the component values for a voltage divider?
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Q50. If a voltage divider is required for a load that will use 450 mA of current, what should be the value of bleeder current?
Q51. If the load in question 50 requires a voltage of +90 V, what should be the value of the bleeder resistor?
Q52. If the source voltage for the voltage divider in question 50 supplies 150 volts, what is the total current through the voltage divider?
A multiple-load voltage divider is shown in figure 3-65. An important point that was not emphasized before is that when using the 10% rule-of-thumb to calculate the bleeder current, you must take 10% of the total load current.
Given the information shown in figure 3-65, you can calculate the values for the resistors needed in the voltage-divider circuits. The same steps will be followed as in the previous voltage divider problem.
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Given:
The bleeder current should be 10% of the total load current.
Solution:
Since the voltage across R1 (ER1) is equal to the voltage requirement for load 1, Ohm’s law can be used to calculate the value for R1.
Solution:
The current through R2 (IR2) is equal to the current through R1 plus the current through load 1. Solution:
The voltage across R2 (ER2) is equal to the difference between the voltage requirements of load 1 and load 2.
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Ohm’s law can now be used to solve for the value of R 2 .
Solution:
The current through R 3 (IR3) is equal to the current through R2 plus the current through load 2.
The voltage across R 3 (ER3) equals the difference between the voltage requirement of load 3 and load 2.
Ohm’s law can now be used to solve for the value of R3.
Solution:
The current through R4 (IR4) is equal to the current through R 3 plus the current through load 3. IR4 is equal to total circuit current (I
T).
The voltage across R4 (ER4) equals the difference between the source voltage and the voltage requirement of load 3.
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Ohm’s law can now be used to solve for the value of R4.
Solution:
With the calculations just explained, the values of the resistors used in the voltage divider are as follows:
Power in the voltage divider is an extremely important quantity. The power dissipated by the resistors in the voltage divider should be calculated to determine the power handling requirements of the resistors. Total power of the circuit is needed to determine the power requirement of the source.
The power for the circuit shown in figure 3-65 is calculated as follows:
Given:
Solution:
The power in each resistor is calculated just as for R 1. When the calculations are performed, the
following results are obtained:
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To calculate the power for load 1:
Given:
Solution:
The power in each load is calculated just as for load 1. When the calculations are performed, the following results are obtained.
Total power is calculated by summing the power consumed by the loads and the power dissipated by the divider resistors. The total power in the circuit is 15.675 watts.
The power used by the loads and divider resistors is supplied by the source. This applies to all electrical circuits; power for all components is supplied by the source.
Since power is the product of voltage and current, the power supplied by the source is equal to the source voltage multiplied by the total circuit current (Es x IT).
In the circuit of figure 3-65, the total power can be calculated by:
Given:
Solution:
VOLTAGE DIVIDER WITH POSITIVE AND NEGATIVE VOLTAGE REQUIREMENTS In many cases the load for a voltage divider requires both positive and negative voltages. Positive
and negative voltages can be supplied from a single source voltage by connecting the ground (reference point) between two of the divider resistors. The exact point in the circuit at which the reference point is placed depends upon the voltages required by the loads.
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For example, a voltage divider can be designed to provide the voltage and current to three loads from a given source voltage.
Given:
The circuit is drawn as shown in figure 3-66. Notice the placement of the ground reference point. The values for resistors R1, R 3, and R4 are computed exactly as was done in the last example. IR1 is the bleeder current and can be calculated as follows:
Solution:
Calculate the value of R1.
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Solution:
Calculate the current through R2 using Kirchhoff’s current law.
At point A:
(or 195mA leaving point A) Since ER2 = E load 2, you can calculate the value of R2.
Solution:
Calculate the current through R 3.
The voltage across R 3 (ER3) equals the difference between the voltage requirements of loads 3 and 2. Solution:
Calculate the value of R3.
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Solution:
Calculate the current through R4.
The voltage across ER4 equals the source voltage (Es) minus the voltage requirement of load 3 and the voltage requirement of load 1. Remember Kirchhoff’s voltage law which states that the sum of the voltage drops and emfs around any closed loop is equal to zero.
Solution:
Calculate the value of R4.
Solution:
With the calculations just explained, the values of the resistors used in the voltage /divider are as follows:
From the information just calculated, any other circuit quantity, such as power, total current, or resistance of the load, could be calculated.
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In actual practice the computed value of the bleeder resistor does not always come out to an even value. Since the rule-of-thumb for bleeder current is only an estimated value, the bleeder resistor can be of a value close to the computed value. (If the computed value of the resistance were 510 ohms, a 500- ohm resistor could be used.) Once the actual value of the bleeder resistor is selected, the bleeder current must be recomputed. The voltage developed by the bleeder resistor must be equal to the voltage requirement of the load in parallel with the bleeder resistor.
The value of the remaining resistors in the voltage divider is computed from the current through the remaining resistors and the voltage across them. These values must be used to provide the required voltage and current to the loads.
If the computed values for the divider resistors are not even values; series, parallel, or series-parallel networks can be used to provide the required resistance.
Example: A voltage divider is required to supply two loads from a 190.5 volts source. Load 1 requires +45 volts and 210 milliamps; load 2 requires +165 volts and 100 milliamps.
Calculate the bleeder current using the rule-of-thumb.
Given:
Solution:
Calculate the ohmic value of the bleeder resistor.
Given:
Solution:
Since it would be difficult to find a resistor of 1451.6 ohms, a practical choice for R1 is 1500 ohms.
Calculate the actual bleeder current using the selected value for R1.
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Given:
Solution:
Using this value for IR1, calculate the resistance needed for the next divider resistor. The current (IR2) is equal to the bleeder current plus the current used by load 1.
Given:
Solution:
The voltage across R2 (ER2) is equal to the difference between the voltage requirements of loads 2 and 1, or 120 volts.
Calculate the value of R2.
Given:
Solution:
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(Es - E load 2) equal to 25.5V. Given:
Solution:
A 75-ohm resistor may not be easily obtainable, so a network of resistors equal to 75 ohms can be used in place of R 3.
Any combination of resistor values adding up to 75 ohms could be placed in series to develop the required network. For example, if you had two 37.5-ohm resistors, you could connect them in series to get a network of 75 ohms. One 50-ohm and one 25-ohm resistor or seven 10-ohm and one 5-ohm resistor could also be used.
A parallel network could be constructed from two 150-ohm resistors or three 225-ohm resistors. Either of these parallel networks would also be a network of 75 ohms.
The network used in this example will be a series-parallel network using three 50-ohm resistors.

Once the values for the various divider resistors have been selected, you can compute the power used by each resistor using the methods previously explained. When the power used by each resistor is known, the wattage rating required of each resistor determines the physical size and type needed for the circuit. This circuit is shown in figure 3-67.
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Q53. In figure 3-67, why is the value of R1 calculated first? Q54. In figure 3-67, how is (a) the current through R2 and (b) the voltage drop across R2 computed? Q55. In figure 3-67, what is the power dissipated in R1? Q56. In figure 3-67, what is the purpose of the series-parallel network R 3, R 4, and R5? Q57. In figure 3-67, what should be the minimum wattage ratings of R 3 and R 5 ? Q58. If the load requirement consists of both positive and negative voltages, what technique is used in
the voltage divider to supply the loads from a single voltage source?
use of formulas derived from Ohm’s law. As in many other fields of science, electricity has its share of special shortcut methods. Some of the special circuit analysis techniques are: THEVENIN’S THEOREM, which uses a process of circuit reduction to Thevenin’s equivalent circuit; and NORTON’S THEOREM, which is reduction of a circuit to Norton’s equivalent. Another method is called LOOP ANALYSIS. This uses Kirchhoff’s voltage law to simultaneously solve problems in parallel branches of a circuit. The use of
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these methods should be reserved until you have become thoroughly familiar with the methods covered thus far in this chapter. You may want to explore some of the special techniques later in your career.
Safety precautions must always be observed by persons working around electric circuits and equipment to avoid injury from electric shock. Detailed safety precautions are contained in NAVMAT P-5l00, Safety Precautions for Shore Activities and OPNAVINST 5l00-19, Navy Safety Precautions for Forces Afloat.
The danger of shock from a 450-volt ac electrical service system is well recognized by operating personnel. This is shown by the relatively low number of reports of serious shock received from this voltage, despite its widespread use. On the other hand, a number of fatalities have been reported due to contact with low-voltage circuits. Despite a fairly widespread, but totally unfounded, popular belief to the contrary, low-voltage circuits (115 volts and below) are very dangerous and can cause death when the resistance of the body is lowered. Fundamentally, current, rather than voltage, is the measure of shock intensity. The passage of even a very small current through a vital part of the human body can cause DEATH. The voltage necessary to produce the fatal current is dependent upon the resistance of the body, contact conditions, the path through the body, etc. For example, when a 60-hertz alternating current, is passed through a human body from hand to hand or from hand to foot, and the current is gradually increased, it will cause the following effects: At about 1 milliampere (0.001 ampere), the shock can be felt; at about 10 milliamperes (0.01 ampere), the shock is of sufficient intensity to prevent voluntary control of the muscles; and at about 100 milliamperes (0.1 ampere) the shock is fatal if it lasts for 1 second or more. The above figures are the results of numerous investigations and are approximate because individuals differ in their resistance to electrical shock. It is most important to recognize that the resistance of the human body cannot be relied upon to prevent a fatal shock from 115 volts or less— FATALITIES FROM VOLTAGES AS LOW AS 30 VOLTS HAVE BEEN RECORDED. Tests have shown that body resistance under unfavorable conditions may be as low as 300 ohms, and possibly as low as 100 ohms from temple to temple if the skin is broken.
Conditions aboard ship add to the chance of receiving an electrical shock. Aboard ship the body is likely to be in contact with the metal structure of the ship and the body resistance may be low because of perspiration or damp clothing. Extra care and awareness of electrical hazards aboard ship are needed.
Short circuits can be caused by accidentally placing or dropping a metal tool, rule, flashlight case, or other conducting article across an energized line. The arc and fire which result, even on relatively low- voltage circuits, may cause extensive damage to equipment and serious injury to personnel.
Since ship service power distribution systems are designed to be ungrounded, many persons believe it is safe to touch one conductor, since no electrical current would flow. This is not true, since the distribution system is not totally isolated from the hull of the ship. If one conductor of an ungrounded electrical system is touched while the body is in contact with the hull of the ship or other metal equipment enclosure, a fatal electric current may pass through the body.
Personnel should constantly be on the alert for any signs which might indicate a malfunction of electric equipment. Besides the more obvious visual signs, the reaction of other senses, such as hearing, smell, and touch, should also make you aware of possible electrical malfunctions. Examples of signs which you must be alert for are: fire, smoke, sparks, arcing, or an unusual sound from an electric motor.
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Frayed and damaged cords or plugs; receptacles, plugs, and cords which feel warm to the touch; slight shocks felt when handling electrical equipment; unusually hot running electric motors and other electrical equipment; an odor of burning or overheated insulation; electrical equipment which either fails to operate or operates irregularly; and electrical equipment which produces excessive vibrations are also indications of malfunctions. When any of the above signs are noted, they are to be reported immediately to a qualified technician. DO NOT DELAY. Do not operate faulty equipment. Above all, do not attempt to make any repairs yourself if you are not qualified to do so. Stand clear of any suspected hazard and instruct others to do likewise.
• Warning Signs—They have been placed for your protection. To disregard them is to invite personal injury as well as possible damage to equipment. Switches and receptacles with a temporary warning tag, indicating work is being performed, are not to be touched.
• Working Near Electrical Equipment—When work must be performed in the immediate vicinity of electrical equipment, check with the technician responsible for the maintenance of the equipment so you can avoid any potential hazards of which you may not be immediately aware.
• Authorized Personnel Only—Because of the danger of fire, damage to equipment, and injury to personnel, all repair and maintenance work on electrical equipment shall be done only by authorized persons. Keep your hands off of all equipment which you have not been specifically authorized to handle. Particularly stay clear of electrical equipment opened for inspection, testing, or servicing.
• Circuit Breakers and Fuses—Covers for all fuse boxes, junction boxes, switch boxes, and wiring accessories should be kept closed. Any cover which is not closed or is missing should be reported to the technician responsible for its maintenance. Failure to do so may result in injury to personnel or damage to equipment in the event accidental contact is made with exposed live circuits.
Carbon dioxide (CO2) is used in fighting electrical fires. It is nonconductive and, therefore, the safest to use in terms of electrical safety. It also offers the least likelihood of damaging equipment. However, if the discharge horn of a CO2 extinguisher is allowed to accidentally touch an energized circuit, the horn may transmit a shock to the person handling the extinguisher.
The very qualities which cause CO2 to be a valuable extinguishing agent also make it dangerous to life. When it replaces oxygen in the air to the extent that combustion cannot be sustained, respiration also cannot be sustained. Exposure of a person to an atmosphere of high concentration of CO2 will cause suffocation.
A person who has stopped breathing is not necessarily dead, but is in immediate danger. Life is dependent upon oxygen, which is breathed into the lungs and then carried by the blood to every body cell. Since body cells cannot store oxygen, and since the blood can hold only a limited amount (and that only for a short time), death will surely result from continued lack of breathing.
However, the heart may continue to beat for some time after breathing has stopped, and the blood may still be circulated to the body cells.  For a very few minutes, there is some chance that the person’s life may be saved.
The process by which a person who has stopped breathing can be saved is called ARTIFICIAL VENTILATION (RESPIRATION).
The purpose of artificial ventilation is to force air out of the lungs and into the lungs, in rhythmic alternation, until natural breathing is reestablished. Artificial ventilation should be given only when natural breathing has stopped; it should NOT be given to any person who is breathing naturally. You should not assume that an individual who is unconscious due to electrical shock has stopped breathing. To tell if someone suffering from an electrical shock is breathing, place your hands on the person’s sides, at the level of the lowest ribs. If the victim is breathing, you will usually be able to feel the movement. Remember: DO NOT GIVE ARTIFICIAL VENTILATION TO A PERSON WHO IS BREATHING NATURALLY.
Records show that seven out of ten victims of electric shock were revived when artificial respiration was started in less than 3 minutes. After 3 minutes, the chances of revival decrease rapidly.
Once it has been determined that breathing has stopped, the person nearest the victim should start the artificial ventilation without delay and send others for assistance and medical aid. The only logical, permissible delay is that required to free the victim from contact with the electricity in the quickest, safest way. This step, while it must be taken quickly, must be done with great care; otherwise, there may be two victims instead of one. In the case of portable electric tools, lights, appliances, equipment, or portable outlet extensions, this should be done by turning off the supply switch or by removing the plug from its receptacle. If the switch or receptacle cannot be quickly located, the suspected electrical device may be pulled free of the victim. Other persons arriving on the scene must be clearly warned not to touch the suspected equipment until it is deenergized. Aid should be enlisted to unplug the device as soon as possible. The injured person should be pulled free of contact with stationary equipment (such as a bus bar) if the equipment cannot be quickly deenergized, or if considerations of military operation or unit survival prevent immediate shutdown of the circuits.
This can be done quickly and safely by carefully applying the following procedures:
1. Protect yourself with dry insulating material.
2. Use a dry board, belt, clothing, or other available nonconductive material to free the victim from electrical contact. DO NOT TOUCH THE VICTIM UNTIL THE SOURCE OF ELECTRICITY HAS BEEN REMOVED.
Once the victim has been removed from the electrical source, it should be determined, if the person is breathing. If the person is not breathing, a method of artificial ventilation is used.
Sometimes victims of electrical shock suffer cardiac arrest (heart stoppage) as well as loss of breathing. Artificial ventilation alone is not enough in cases where the heart has stopped. A technique known as Cardiopulmonary Resuscitation (CPR) has been developed to provide aid to a person who has stopped breathing and suffered a cardiac arrest. Because you most likely will be working in the field of electricity, the risk of electrical shock is higher than most other Navy occupations. You should, at your earliest opportunity, learn the technique of CPR.
CPR is relatively easy to learn and is taught in courses available from the American Red Cross, some Navy Medical Departments, and in the Standard First Aid Training Course (NAVEDTRA 12081).
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Q59. Is it considered safe for a person to touch any energized low-voltage conductor with the bare hand?
Q60. What should you do if you become aware of a possible malfunction in a piece of electrical equipment?
Q61. Who should perform CPR?
With the completion of this chapter you have gained a basic understanding of dc circuits. The information you have learned will provide you with a firm foundation for continuing your study of electricity. The following is a summary of the important points in the chapter.
A BASIC ELECTRIC CIRCUIT consists of a source of electrical energy connected to a load. The load uses the energy and changes it to a useful form.
A SCHEMATIC DIAGRAM is a "picture" of a circuit, which uses symbols to represent components. The space required to depict an electrical or electronic circuit is greatly reduced by the use of a schematic.
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VOLTAGE (E) is the electrical force or pressure operating in a circuit. AN AMPERE (A) represents the current flow produced by one volt working across one ohm of
resistance.
RESISTANCE (R)�LV�WKH�RSSRVLWLRQ�WR�FXUUHQW��,W�LV�PHDVXUHG�LQ�RKPV�� ���2QH�RKP�RI�UHVLVWDQFH will limit the current produced by one volt to a level of one ampere.
THE OHM’S FORMULA can be transposed to find one of the values in a circuit if the other two values are known. You can transpose the Ohm’s law formula
mathematically, or you can use the Ohm’s law figure to determine the mathematical relationship between R, E, and I.
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GRAPHICAL ANALYSIS of the relationship between R, E, and I can be studied by plotting these quantities on a graph. Such a graph is useful for observing the characteristics of an electrical device.
POWER is the rate of doing work per unit of time. The time required to perform a given amount of work will determine the power expended. As a formula, P = E x I, where P = power in watts, E = voltage in volts, and I = current in amperes.
THE FOUR BASIC ELECTRICAL QUANTITIES are P, I, E, R. Any single unknown quantity can be expressed in terms of any two of the other known quantities. The formula wheel is a simple representation of these relationships.
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POWER RATING in watts indicates the rate at which a device converts electrical energy into another form of energy. The power rating of a resistor indicates the maximum power the resistor can withstand without being destroyed.
POWER USED by an electrical device is measured in watt-hours. One watt-hour is equal to one watt used continuously for one hour.
THE EFFICIENCY of an electrical device is equal to the electrical power converted into useful energy divided by the electrical power supplied to the device.
HORSEPOWER is a unit of measurement often used to rate electrical motors. It is a unit of work. One horsepower is equal to 746 watts.
A SERIES CIRCUIT is defined as a circuit that has only one path for current flow.
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RULES FOR SERIES DC CIRCUITS:
• The same current flows through each part of a series circuit.
• The total resistance of a series circuit is equal to the sum of the individual resistances.
• The total voltage across a series circuit is equal to the sum of the individual voltage drops.
• The voltage drop across a resistor in a series circuit is proportional to the ohmic value of the resistor.
• The total power in a series circuit is equal to the sum of the individual power used by each circuit component.
KIRCHHOFF’S VOLTAGE LAW states: The algebraic sum of the voltage drops in any closed path in a circuit and the electromotive forces in that path is equal to zero, or Ea + Eb + Ec +...En = 0.
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VOLTAGE POLARITIES must be used when applying Kirchhoff’s voltage law. The point at which current enters a load (resistor) is considered negative with respect to the point at which current leaves the load.
SERIES AIDING VOLTAGES cause current to flow in the same direction; thus the voltages are added.
SERIES OPPOSING VOLTAGES tend to force current to flow in opposite directions; thus the equivalent voltage is the difference between the opposing voltages.
A REFERENCE POINT is a chosen point in a circuit to which all other points are compared.
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AN OPEN CIRCUIT is one in which a break exists in the complete conducting pathway.
A SHORT CIRCUIT is an accidental path of low resistance which passes an abnormally high amount of current.
INTERNAL RESISTANCE causes a drop in the terminal voltage of a source as current flows through the source. The decrease in terminal voltage is caused by the voltage drop across the internal resistance. All sources of electromotive force have some form of internal resistance.
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HIGH EFFICIENCY in a circuit is achieved when the resistance of the load is high with respect to the resistance of the source.
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POWER TRANSFER in a circuit is highest when the resistance of the load equals the resistance of the source.
A PARALLEL CIRCUIT is a circuit having more than one current path connected to a common voltage source.
RULES FOR PARALLEL DC CIRCUITS:
• The same voltage exists across each branch of a parallel circuit and is equal to the source voltage.
• The current through a branch of a parallel network is inversely proportional to the amount of resistance of the branch.
• The total current of a parallel circuit is equal to the sum of the currents of the individual branches of the circuit.
• The total resistance of a parallel circuit is equal to the reciprocal of the sum of the reciprocals of the individual resistances of the circuit.
• The total power consumed in a parallel circuit is equal to the sum of the power consumptions of the individual resistances.
THE SOLUTION OF A COMBINATION CIRCUIT is a matter of applying the laws and rules for series and parallel circuits as applicable.
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ALL PARALLEL CIRCUITS ARE COMBINATION CIRCUITS when the internal resistance of the source is taken into account.
REDRAWING CIRCUITS FOR CLARITY is accomplished in the following steps:
1. Trace the current paths in the circuit.
2. Label the junctions in the circuit. 3. Recognize points which are at the same potential.
4. Visualize rearrangements, "stretching" or "shrinking," of connecting wires.
5. Redraw the circuit into simpler form (through stages if necessary).
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EQUIPMENT PROTECTION from short-circuit current is accomplished by use of fuses and other circuit protection devices.
A VOLTAGE DIVIDER is a series circuit in which desired portions of the source voltage may be tapped off for use in equipment. Both negative and positive voltage can be provided to the loads by the proper selection of the reference point (ground).
3-122
ELECTRICAL SAFETY PRECAUTIONS must be observed. A fatal shock can occur from 0.1 ampere of current. Voltages as low as 30 volts have been recorded as causing sufficient current to be fatal.
ALL LIVE ELECTRICAL CIRCUITS shall be treated as potential hazards at all times.
ELECTRONIC OR ELECTRICAL EQUIPMENT discovered to be faulty or unsafe should be reported immediately to proper authority.
ELECTRICAL OR ELECTRONIC EQUIPMENT should be used and repaired by authorized personnel only.
A CO2 EXTINGUISHER should be used to extinguish electrical fires.
FIRST AID FOR ELECTRICAL SHOCK includes the following actions:
• Remove the victim from the source of the shock.
• Check the victim to see if the person is breathing.
• If the victim is not breathing, give artificial ventilation. The preferred method is mouth-to-mouth.
• CPR may be necessary if the heartbeat has stopped, but do not attempt this unless you have been trained in its use. OBTAIN MEDICAL ASSISTANCE AS SOON AS POSSIBLE.
3-123
ANSWERS TO QUESTIONS Q1. THROUGH Q61. A1. (a) DS1, the flashlight bulb (b) BAT, the dry cell A2. The path for current is incomplete; or, there is no path for current with S1 open. A3. A schematic diagram.
A4. (a) Current increases (b) Current decreases A5. (a) Current decreases (b) Current increases A6.
A7. 1.25 amperes.
A8. 4 amperes.
A9. Power.
A10. By changing the circuit resistance or the voltage of the power source. A11.
A12. 6 amperes.
A13. A wirewound resistor.
A14. 1 kilowatt.
A15. 8,952 watt hours or 8.952 kWh.
A16. 942 (rounded to 3 places). A17.
3-124
A18.
A19.
A20. The source voltage would have to be increased to 640 volts.
A21.
A22. The point at which current enters the resistor is assigned a negative polarity and the point at which current leaves the resistor is assigned a positive polarity.
A23. 2 amperes.
A24. 120 volts.
A25. 50 volts.
A26. Zero volts.
A27. A circuit where there is no longer a complete path for current flow. A28. An accidental path of low resistance which passes an abnormally high amount of current. A29. The internal (source) resistance of the battery will drop some of the voltage. A30. When the load resistance equals the source resistance.
A31. 50 percent.
3-125
A32.
A33. 60 volts.
A34. Total current in a series circuit flows through every circuit component but in a parallel circuit total current divides among the available paths.
A35. Whether the current is entering the junction (+) or leaving the junction (-). A36.
A37.
A38.
A39. Equivalent resistor or Req.
A40. In both cases all the power used in the circuit must come from the source. A41.
A42. PT = 60 W, ER2 = 10 V.
A43. � �
A44. �� �
3-126
A45. Because of the 2-volt drop across the internal resistance, only 48 volts is available for the rest of the circuit.
A46. (a) Total resistance increases, total current decreases (b) Total resistance becomes infinite, total current is equal to zero
A47. (a) Total resistance decreases, total current increases (b) Total resistance decreases, total current increases
A48. None.
A49. The source voltage and load requirements (voltage and current). A50. 45 mA rule-of-thumb. A51. 2 N �
A52. 495 mA.
A53. R1 is the bleeder resistor. Bleeder current must be known before any of the remaining divider resistor ohmic values can be computed.
A54. (a) By adding the bleeder current (IR1) and the current through load 1(b) By subtracting the voltage of load 1 from the voltage of load 2.
A55. 1.35 watts.
A56. The series-parallel network drops the remaining source voltage and is used to take the place of a single resistor (75 ohms) when the required ohmic value is not available in a single resistor.
A57. R3 = 2 watts; R5 = 6 watts.
A58. The ground (reference point) is placed in the proper point in the voltage divider so that positive and negative voltages are supplied.
A59. NEVER! All energized electric circuits should be considered potentially dangerous.
A60. You should immediately report this condition to a qualified technician. A61. Only trained, qualified personnel.
AI-1
AMMETER—An instrument for measuring the amount of electron flow in amperes.
AMPERE—The basic unit of electrical current.
ANODE—A positive electrode of an electrochemical device (such as a primary or secondary electric cell) toward which the negative ions are drawn.
ATTRACTION—The force that tends to make two objects approach each other. Attraction exists between two unlike magnetic poles (North and South) or between two unlike static charges (plus and minus).
BATTERY—A device for converting chemical energy into electrical energy.
BATTERY CAPACITY—The amount of energy available from a battery. Battery capacity is expressed in ampere-hours.
BLEEDER CURRENT—The current through a bleeder resistor. In a voltage divider, bleeder current is usually determined by the 10 percent rule of thumb.
BLEEDER RESISTOR—A resistor which is used to draw a fixed current.
BRANCH—An individual current path in a parallel circuit.
CATHODE—The general name for any negative electrode.
CELL—A single unit that transforms chemical energy into electrical energy. Batteries are made up of cells.
CHARGE—Represents electrical energy. A material having an excess of electrons is said to have a negative charge. A material having a deficiency of electrons is said to have a positive charge.
CIRCUIT—The complete path of an electric current.
CIRCULAR MIL—An area equal to that of a circle with a diameter of 0.001 inch. It is used for measuring the cross-sectional area of wires.
COMBINATION CIRCUIT—A series-parallel circuit.
CONDUCTANCE—The ability of a material to conduct or carry an electric current. It is the reciprocal of the resistance of the material, and is expressed in mhos or siemans.
CONDUCTIVITY—Ease with which a substance transmits electricity.
CONDUCTOR—(1) A material with a large number of free electrons. (2) A material which easily permits electric current to flow.
COULOMB—A measure of the quantity of electricity. One coulomb is equal to 6.28 · 1018 electrons.
AI-2
COULOMB’S LAW—Also called the law of electric charges or the law of electrostatic attraction. Coulomb's Law states that charged bodies attract or repel each other with a force that is directly proportional to the product of their individual charges and inversely proportional to the square of the distance between them.
CPR—Cardio-Pulminary Resuscitation.
CROSS-SECTIONAL AREA—The area of a "slice" of an object. When applied to electrical conductors, it is usually expressed in circular mils.
CURRENT—The flow of electrons past a reference point. The passage of electrons through a conductor. Measured in amperes.
DEAD SHORT—A short circuit having minimum resistance.
DIELECTRIC FIELD—The space between and around charged bodies in which their influence is felt. Also called Electric Field of Force or an Electrostatic Field.
DIRECT CURRENT—An electric current that flows in one direction only.
DOMAIN THEORY—A theory of magnetism based upon the electron-spin principle. Spinning electrons have a magnetic field. If more electrons spin in one direction than another, the atom is magnetized.
DRY CELL—An electrical cell in which the electrolyte is not a liquid. In most dry cells the electrolyte is in the form of a paste.
EFFICIENCY—The ratio of output power to input power, generally expressed as a percentage.
ELECTRIC CURRENT—The flow of electrons.
ELECTRICAL CHARGE—Symbol Q, q. Electric energy stored on or in an object. The negative charge is caused by an excess of electrons; the positive charge is caused by a deficiency of electrons.
ELECTROCHEMICAL—The action of converting chemical energy into electrical energy.
ELECTRODE—The terminal at which electricity passes from one medium into another, such as in an electrical cell where the current leaves or returns to the electrolyte.
ELECTROLYTE—A solution of a substance which is capable of conducting electricity. An electrolyte may be in the form of either a liquid or a paste.
ELECTROMAGNET—An electrically excited magnet capable of exerting mechanical force, or of performing mechanical work.
ELECTROMAGNETIC—The term describing the relationship between electricity and magnetism. Having both magnetic and electric properties.
ELECTROMAGNETIC INDUCTION—The production of a voltage in a coil due to a change in the number of magnetic lines of force (flux linkages) passing through the coil.
ELECTRON—The elementary negative charge that revolves around the nucleus of an atom.
ELECTRON SHELL—A group of electrons which have a common energy level that forms part of the outer structure (shell) of an atom.
AI-3
ELECTROSTATIC—Pertaining to electricity at rest, such as charges on an object (static electricity). ELEMENT—A substance, in chemistry, that cannot be divided into simpler substances by any means
ordinarily available.
EMF—(Electromotive Force) The force which causes electricity to flow between two points with different electrical charges or when there is a difference of potential between the two points. The unit of measurement in volts.
ENERGY—The ability or capacity to do work.
EQUIVALENT RESISTANCE—(Req) A resistance that represents the total ohmic values of a circuit component or group of circuit components. Usually drawn as a single resistor when simplifying complex circuits.
FERROMAGNETIC MATERIAL—A highly magnetic material, such as iron, cobalt, nickel, or alloys, make up these materials.
FIELD OF FORCE—A term used to describe the total force exerted by an action-at-a-distance phenomenon such as gravity upon matter, electric charges acting upon electric charges, magnetic forces acting upon other magnets or magnetic materials.
FIXED RESISTOR—A resistor having a definite resistance value that cannot be adjusted. FLUX—In electrical or electromagnetic devices, a general term used to designate collectively all the
electric or magnetic lines of force in a region.
FLUX DENSITY—The number of magnetic lines of force passing through a given area.
GAS—One of the three states of matter having no fixed form or volume. (Steam is a gas.) GRAPH—A pictorial presentation of the relation between two or more variable quantities, such as
between an applied voltage and the current it produces in a circuit.
GROUND POTENTIAL—Zero potential with respect to the ground or earth.
HORSEPOWER—The English unit of power, equal to work done at the rate of 550 foot-pounds per second. Equal to 746 watts of electrical power.
HORSESHOE MAGNET—A permanent magnet or electromagnet bent into the shape of a horseshoe or having a U-shape to bring the two poles near each other.
HYDROMETER—An instrument used to measure specific gravity. In batteries hydrometers are used to indicate the state of charge by the specific gravity of the electrolyte.
INDUCED CHARGE—An electrostatic charge produced on an object by the electric field that surrounds a nearby object.
INDUCED CURRENT—Current due to the relative motion between a conductor and a magnetic field.
INDUCED ELECTROMOTIVE FORCE—The electromotive force induced in a conductor due to the relative motion between a conductor and a magnetic field.
INDUCED VOLTAGE—See Induced Electromotive Force.
AI-4
INDUCTION—The act or process of producing voltage by the relative motion of a magnetic field across a conductor.
INFINITE—(1) Extending indefinitely, endless. (2) Boundless having no limits. (3) An incalculable number.
INSULATION—(1) A material used to prevent the leakage of electricity from a conductor and to provide mechanical spacing or support to protect against accidental contact. (2) Use of material in which current flow is negligible to surround or separate a conductor to prevent loss of current.
INSULATOR—(1) Material of such low conductivity that the flow of current through it can usually be neglected. (2) Device having high-electric resistance, used for supporting or separating conductors so as to prevent undesired flow of current from the conductors to other objects.
INVERSELY—Inverted or reversed in position or relationship.
ION—An electrically charged atom or group of atoms. Negative ions have an excess of electrons; positive ions have a deficiency of electrons.
IONIZE—To make an atom or molecule of an element lose an electron, as by X-ray bombardment, and thus be converted into a positive ion. The freed electron may attach itself to a neutral atom or molecule to form a negative ion.
JUNCTION—(1) The connection between two or more conductors. (2) The contact between two dissimilar metals or materials, as is in a thermocouple.
KILO—A prefix meaning one thousand.
KINETIC ENERGY—Energy which a body possesses by virtue of its motion.
KIRCHHOFF’S LAWS—(1) The algebraic sum of the currents flowing toward any point and the current flowing from that point in an electric network is zero. (2) The algebraic sum of the products of the current and resistance in each of the conductors in any closed path in a network is equal to the algebraic sum of the electromotive forces in the path.
LAW OF MAGNETISM—Like poles repel; unlike poles attract.
LEAD-ACID CELL—A cell in an ordinary storage battery, in which electrodes are grids of lead containing an active material consisting of certain lead oxides that change in composition during charging and discharging. The electrodes or plates are immersed in an electrolyte of diluted sulfuric acid.
LINE OF FORCE—A line in an electric or magnetic field that shows the direction of the force.
LIQUID—One of the three states of matter which has a definite volume but no definite form. (Water is a liquid.)
LOAD—(1) A device through which an electric current flows and which changes electrical energy into another form. (2) Power consumed by a device or circuit in performing its function.
LOCAL ACTION—A continuation of current flow within an electrical cell when there is no external load. Caused by impurities in the electrode.
MAGNETIC FIELD—The space in which a magnetic force exists.
AI-5
MAGNETIC POLES—The section of a magnet where the flux lines are concentrated; also where they enter and leave the magnet.
MAGNETISM—The property possessed by certain materials by which these materials can exert mechanical force on neighboring masses of magnetic materials; and can cause currents to be induced in conducting bodies moving relative to the magnetized bodies.
MATTER—Any physical entity which possesses mass.
MEGA—A prefix meaning one million, also Meg.
MHO—Unit of conductance: the reciprocal of the ohm. Replaced by siemens.
MICRO—A prefix meaning one-millionth.
MILLI—A prefix meaning one-thousandth.
NEGATIVE ELECTRODE—A terminal or electrode having more electrons than normal. Electrons flow out of the negative terminal of a voltage source.
NEGATIVE TEMPERATURE COEFFICIENT—The temperature coefficient expressing the amount of reduction in the value of a quantity, such as resistance for each degree of increase in temperature.
NETWORK—A combination of electrical components. In a parallel circuit it is composed of two or more branches.
NEUTRAL—In a normal condition, hence neither positive nor negative. A neutral object has a normal number of electrons.
OHM—The unit of electrical resistance. It is that value of electrical resistance through which a constant potential difference of 1 volt across the resistance will maintain a current flow of 1 ampere through the resistance.
OHMIC VALUE—Resistance in ohms.
OHM’S LAW—The current in an electric circuit is directly proportional to the electromotive force in the circuit. The most common form of the law is E = IR, where E is the electromotive force or voltage across the circuit, I is the current flowing in the circuit, and R is the resistance of the circuit.
OPEN CIRCUIT—(1) The condition of an electrical circuit caused by the breaking of continuity of one or more conductors of the circuit; usually an undesired condition. (2) A circuit which does not provide a complete path for the flow of current.
PARALLEL CIRCUIT—Two or more electrical devices connected to the same pair of terminals so separate currents flow through each; electrons have more than one path to travel from the negative to the positive terminal.
PERMEABILITY—The measure of the ability of a material to act as a path for magnetic lines of force.
PHOTOELECTRIC VOLTAGE—A voltage produced by light.
PICO—A prefix adopted by the National Bureau of Standards meaning 10 –12.
AI-6
PIEZOELECTRIC EFFECT—The effect of producing a voltage by placing a stress, either by compression, expansion, or twisting, on a crystal and, conversely, producing a stress in a crystal by applying a voltage to it.
PLATE—One of the electrodes in a storage battery.
POLARITY—(1) The condition in an electrical circuit by which the direction of the flow of current can be determined. Usually applied to batteries and other direct voltage sources. (2) Two opposite charges, one positive and one negative. (3) A quality of having two opposite magnetic poles, one north and the other south.
POLARIZATION—The effect of hydrogen surrounding the anode of a cell which increases the internal resistance of the cell.
POTENTIAL ENERGY—Energy due to the position of one body with respect to another body or to the relative parts of the same body.
POTENTIOMETER—A 3-terminal resistor with one or more sliding contacts, which functions as an adjustable voltage divider.
POWER—The rate of doing work or the rate of expending energy. The unit of electrical power is the watt.
PRIMARY CELL—An electrochemical cell in which the chemical action eats away one of the electrodes, usually the negative electrode.
RECIPROCAL—The value obtained by dividing the number 1 by any quantity.
REFERENCE POINT—A point in a circuit to which all other points in the circuit are compared.
RELUCTANCE—A measure of the opposition that a material offers to magnetic lines of force.
REPULSION—The mechanical force tending to separate bodies having like electrical charges or like magnetic polarity.
RESIDUAL MAGNETISM—Magnetism remaining in a substance after removal of the magnetizing force.
RESISTANCE—(1) The property of a conductor which determines the amount of current that will flow as the result of the application of a given electromotive force. All conductors possess some resistance, but when a device is made especially for the purpose of limiting current flow, it is called a resistor. A resistance of 1 ohm will allow a current of 1 ampere to flow through it when a potential of 1 volt is applied. (2) The opposition which a device or material offers to the flow of current. The effect of resistance is to raise the temperature of the material or device carrying the current. (3) A circuit element designed to offer a predetermined resistance to current flow.
RESISTOR—The electrical component which offers resistance to the flow of current. It may be a coil of fine wire or a composition rod.
RETENTIVITY—The ability of a material to retain its magnetism.
RHEOSTAT—(1) A resistor whose value can be varied. (2) A variable resistor which is used for the purpose of adjusting the current in a circuit.
AI-7
SCHEMATIC CIRCUIT DIAGRAM—A circuit diagram in which component parts are represented by simple, easily drawn symbols. May be called schematic.
SCHEMATIC SYMBOLS—A letter, abbreviation, or design used to represent specific characteristics or components on a schematic diagram.
SECONDARY CELL—A cell that can be recharged by passing a current through the cell in a direction opposite to the discharge current.
SERIES CIRCUIT—An arrangement where electrical devices are connected so that the total current must flow through all the devices; electrons have one path to travel from the negative terminal to the positive terminal.
SERIES-PARALLEL CIRCUIT—A circuit that consists of both series and parallel networks.
SHELF LIFE—The period of time that a cell or battery may be stored and still be useful.
SHIELDING—A metallic covering used to prevent magnetic or electromagnetic fields from effecting an object.
SHORT CIRCUIT—A low resistance connection between two points of different potential in a circuit, usually accidental and usually resulting in excessive current flow that may cause damage.
SIEMANS—The new and preferred term for mho.
SOLID—One of the three states of matter which has definite volume and shape. (Ice is a solid.) SOURCE VOLTAGE—The device which furnishes the electrical energy used by a load.
SPECIFIC GRAVITY—The ratio between the density of a substance and that of pure water at a given temperature.
STATIC ELECTRICITY—Stationary electricity that is in the form of a charge. The accumulated electric charge on an object.
SWITCH—A device to connect, disconnect, or change the connections in an electrical circuit.
TAPPED RESISTOR—A wire-wound, fixed resistor having one or more additional terminals along its length, generally for voltage-divider applications.
TEMPERATURE COEFFICIENT—The amount of change of resistance in a material per unit change in temperature.
TERMINAL—An electrical connection.
THERMOCOUPLE—A junction of two dissimilar metals that produces a voltage when heated. TOLERANCE—(1) The maximum error or variation from the standard permissible in a measuring
instrument. (2) A maximum electrical or mechanical variation from specifications which can be tolerated without impairing the operation of a device.
AI-8
TOTAL RESISTANCE—(RT) The equivalent resistance of an entire circuit. For a series circuit: RT = R1 + R2 + R3 . . . Rn. For parallel circuits:
UNIDIRECTIONAL—In one direction only.
VALENCE—The measure of the extent to which an atom is able to combine directly with other atoms. It is believed to depend on the number and arrangement of the electrons in the outermost shell of the atom.
VALENCE SHELL—The electrons that form the outermost shell of an atom.
VARIABLE RESISTOR—A wire-wound or composition resistor, the value of which may be changed.
VOLT—The unit of electromotive force or electrical pressure. One volt is the pressure required to send 1 ampere of current through a resistance of 1 ohm.
VOLTAGE—(1) The term used to signify electrical pressure. Voltage is a force which causes current to flow through an electrical conductor. (2) The voltage of a circuit is the greatest effective difference of potential between any two conductors of the circuit
VOLTAGE DIVIDER—A series circuit in which desired portions of the source voltage may be tapped off for use in equipment.
VOLTAGE DROP—The difference in voltage between two points. It is the result of the loss of electrical pressure as a current flows through a resistance.
WATT—The practical unit of electrical power. It is the amount of power used when one ampere of dc flows through a resistance of one ohm.
WATTAGE RATING—A rating expressing the maximum power that a device can safely handle.
WATT-HOUR—A practical unit of electrical energy equal to one watt of power for one hour.
WEBER’S THEORY—A theory of magnetism which assumes that all magnetic material is composed of many tiny magnets. A piece of magnetic material that is magnetized has all of the tiny magnets aligned so that the north pole of each magnet points in one direction.
WIRE—A solid or stranded group of solid, cylindrical conductors having low resistance to current flow, with any associated insulation.
WORK—The product of force and motion.
AII-1
The International Symbols Committee has adopted prefixes for denoting decimal multiples of units. The National Bureau of Standards has followed the recommendations of this committee, and has adopted the following list of prefixes:
.1 10-1 deci d
.01 10-2 centi c
.001 10-3 milli m
.000001 10-6 micro u
.000000001 10-9 nano n
.000000000001 10-12 Pico p
.000000000000001 10-15 femto F
.000000000000000001 10-18 atto a
To multiply like (with same base) exponential quantities, add the exponents. In the language of algebra the rule is am · a n = am+n
AII-2
To divide exponential quantities, subtract the exponents. In the language of algebra the rule is
*Generally used with electrical quantities.
To raise an exponential quantity to a power, multiply the exponents. In the language of algebra (xm)n = xmn.
Any number (except zero) raised to the zero power is one. In the language of algebra x0 = 1
Any base with a negative exponent is equal to 1 divided by the base with an equal positive exponent. In the language of algebra x –a = 1/xa
To raise a product to a power, raise each factor of the product to that power.
AII-3
To find the nth root of an exponential quantity, divide the exponent by the index of the root. Thus, the nth root of am = am/n.
AIV-1
INDEX-1
INDEX-2
3-9 to 3-12 parallel d.c. circuits, 3-49 to 3-78
series d.c. circuits, 3-19 to 3-33 analysis, 3-28 to 3-33 characteristics, 3-19 summary, 3-28
series-parallel d.c. circuits, 3-76 to 3-84 effects of open and short circuits, 3-89
INDEX-3
F Ferromagnetic materials, 1-14 First aid for electric shock, 3-109, 3-110 Fixed and variable resistors, 1-42 Formulas, d.c. circuits, AV-1 G Glossary, Al-I to AI-9 H Hydrometer, battery, 2-19 K Kirchhoff’s voltage law, 3-34 to 3-43
INDEX-4
P Parallel d.c. circuits, 3-49 to 3-78
Secondary cell, batteries, 2-3 Secondary cell chemistry, 2-5, 2-6 Series-connected cells, 2-13, 2-14 Series d.c. circuits, 3-19 to 3-33
Series d.c. circuits—Continued analysis, 3-28 to 3-33 characteristics, 3-19
Series-parallel-connected cells, 2-14 Series-parallel d.c. circuits, 3-76 to 3-91
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
Textbook assignment: Chapter 1, Turning to Electricity, pages 1-1 through 1-65.
1-1. Matter can be found in which of the
following forms?
1. Solid
2. Liquid
3. Gaseous
4. Each of the above
1-2. A substance that CANNOT be reduced to a
1. element
2. mixture
3. compound
4. solution
1-3. A molecule is the smallest possible particle
the following substances?
1. An element
2. A mixture
3. A compound
4. A solution
1-4. An atom is the smallest possible particle
the following substances?
1. An element
2. A mixture
3. A compound
4. A solution
1-5. What subatomic particle has a negative
charge and a small mass?
1. Proton
2. Electron
3. Positron
4. Neutron
1-6. What subatomic particle has a positive
charge and a large mass?
1. Proton
2. Electron
3. Positron
4. Neutron
1-7. What subatomic particle has no charge?
1. Proton
2. Electron
3. Positron
4. Neutron
1-8. When light is represented as a tiny packet
called?
1. Angstroms
2. Photons
3. Wavelengths
4. Frequencies
1-9. If light energy collides with an orbiting
electron, what happens to the electron?
1. The electron will move around the
2. The electron will jump to an orbit
3. The electron will jump to an orbit
4. The electron will merge with the
2
1-10. After the action described in question 1-9
the light. When the electron returns to this
occurs?
1. The nucleus becomes lighter
2. The atom becomes an ion
3. Light energy is emitted
4. The valence of the atom changes
1-11. The number of electrons in the outermost
following characteristics of the atom?
1. Valence
2. Atomic weight
3. Atomic number
4. Number of shells
1-12. When an atom gains or loses an electron,
which of the following terms applies?
1. Unbalanced
2. Lightened
3. Neutral
4. Ionized
1-13. What is the main difference between
insulators?
1. The temperature differences
2. The physical state of their mass
3. The number of free electrons
4. The designations of the outer shells
1-14. A substance with an excess of electrons is
considered to be in what electrical state?
1. Neutral
2. Positive
3. Negative
4. Discharged
1-15. Which of following actions describes the
charge?
1. Friction between two conductors
2. Friction between two insulators
3. Pressure between two conductors
4. Pressure between two insulators
1-16. An atom that contains 6 protons and 5
electrons has what electrical charge?
1. Positive
2. Negative
3. Neutral
4. Intermediate
1-17. How do "like" and "unlike" charges react to
one another?
1. Unlike charges repel each other, like
2. Unlike charges attract each other, like
3. Unlike charges repel each other, like
4. Unlike charges attract each other, like
1-18. What is/are the term(s) applied to the space
which their influence is felt?
1. Electric field of force
2. Electrostatic field
3. Dielectric field
4. Each of the above
1-19. Electrostatic lines of force are drawn in
which of the following manners?
1. Entering negative charge, entering
2. Entering negative charge, leaving
3. Leaving negative charge, leaving
4. Leaving negative charge, entering
3
1-20. Which of the following devices use
magnetism?
1. Batteries
2. Light bulbs
3. High-fidelity speakers
4. Each of the above
1-21. Magnetic materials have which of the
following qualities?
1. They are attracted by magnets
2. They can be magnetized
3. Both 1 and 2 above
4. They are electrical insulators
1-22. Ferromagnetic materials have which of the
following qualities?
1. They are all alloys
2. They all contain nickel
3. They make very weak magnets
4. They are relatively easy to magnetize
1-23. A material with low reluctance and high
used to make what type of magnet?
1. Temporary
2. Permanent
3. Residual
4. Natural
1-24. The ability of a material to retain
1. permeability
2. retentivity
3. reluctance
4. ionization
1-25. The law of magnetic poles states which of
the following relationships?
1. Like poles attract, unlike poles attract
2. Like poles attract, unlike poles repel
3. Like poles repel, unlike poles repel
4. Like poles repel, unlike poles attract
1-26. The north indicating pole of a compass
following poles of the earth?
1. The geographic north pole
2. The magnetic north pole
3. The geographic south pole
4. The magnetic south pole
1-27. Weber's theory of magnetism assumes that
1. tiny molecular magnets
2. domains of magnetic influence
3. large blocks of material acting as
4. atoms with electrons spinning different
1-28. According to the domain theory, if an atom
1. charged
2. insulated
3. neutralized
4. magnetized
1-29. If a glass plate is placed over a magnet and
pattern will be visible. What does this
pattern indicate?
1. The magnetic field
2. The electrostatic field
3. The piezoelectric effect
4. The chemical reaction of the magnet
1-30. An imaginary line used to illustrate a
1. magnetic pole
2. force field pole
3. magnetic line of force
4. electrostatic line of force
4
1-31. Which of the following is NOT a property
of magnetic lines of force?
1. They form closed loops around the
2. They leave the magnetic material at
3. They cross each other at right angles
4. They leave the north pole and enter the
1-32. A magnetic shield or screen used to protect
which of the following materials?
1. Plastic
2. Copper
3. Soft iron
4. Aluminum
1-33. Bar magnets should be stored in which of
the following manners?
1. Separately
2. In pairs at 90 degree angles
3. In pairs with north poles together
4. In pairs with a north pole and a south
1-34. What is the term applied to the ability to do
work?
1. Power
2. Energy
3. Voltage
4. Current
1-35. An object that is in motion has what type of
energy?
1. Kinetic
2. Magnetic
3. Newtonian
4. Potential
1-36. A book sitting on a shelf has what kind of
energy?
1. Kinetic
2. Potential
3. Newtonian
4. Magnetic
1-37. Which of the following term(s) apply(ies)
bodies?
1. Voltage
2. Electromotive force
3. Both 1 and 2 above
4. Current
1-38. Which of the following terms is equal to
"2.1 kV?"
1. 210 V
2. 2100 V
3. 21,000 V
4. 2.1 x 106 V
1-39. 250µV is equal to which of the following
terms?
1. .25 mV
2. .00025 V
3. 250 x 10-6 V
4. All of the above
1-40. What is the general term that describes a
device which supplies a voltage?
1. A voltage source
2. A voltage supply
3. A voltage generator
4. A voltage producer
1-41. In addition to friction, magnetism, and
methods can be used to produce a voltage?
1. Pressure
2. Heat
3. Light
4. Each of the above
5
B TO THE DEVICE LISTED IN COLUMN A.
1-42. Radio receiver's
1. Heat
1-43. Thermocouple 2. Pressure
1-44. Automobile battery 3. Magnetism
1-45. Automobile generator 4. Chemical action
1-46. Flashlight cell
1-47. Current in an electric circuit is caused by
which of the following actions?
1. Electrons moving from negative to
2. Electrons moving from positive to
3. Protons moving from negative to
4. Protons moving from positive to
1-48. When directed drift takes place, at what
speed does the effect take place?
1. 100,000 miles per hour
2. 186,000 miles per second
3. 300,000 meters per hour
4. 500,000 meters per second
1-49. If the voltage in a circuit increases, what
happens to the current?
1. Current increases
2. Current decreases
3. Current remains the same
4. Current fluctuates rapidly
1-50. Which of the following values is equal to
100mA?
1. 1.0 ampere
2. 10.0 amperes
3. 0.10 ampere
4. 0.01 ampere
1-51. What symbol is used to represent the ohm?
1. A
2. O
3. µ
4. !
1-52. If low weight is the major factor, which of
conductor?
1. Aluminum
2. Copper
3. Silver
4. Gold
1-53. What material is MOST widely used as a
conductor in electrical equipment?
1. Aluminum
2. Copper
3. Silver
4. Gold
1-54. Resistance of a conductor will increase with
conductor?
1. Cross-sectional area is increased, length
2. Cross-sectional area is increased, length
3. Cross-sectional area is decreased,
4. Cross-sectional area is decreased,
6
1-55. A material whose resistance decreases as
temperature coefficient?
1. Positive
2. Negative
3. Zero
4. Neutral
1-56. A material whose resistance remains
what temperature coefficient?
1. Positive
2. Negative
3. Zero
4. Neutral
1-57. Which of the following units is NOT a unit
of conductance?
1. Siemens
2. S
3. G
4. Ohm
1-58. Resistance bears which, if any, of the
following relationships to conductance?
1. A direct relationship
2. A reciprocal relationship
3. An inverse square relationship
4. None
INTENTIONALLY.
1-59. Which of the following schematic symbols
is used to represent a resistor?
1-60. How is the ability of a resistor to dissipate
heat indicated?
1. By the wattage rating
2. By the voltage rating
3. By the resistance rating
4. By the tolerance
1-61. Carbon resistors have which of the
following disadvantages?
1. A high cost factor
2. An extremely large physical size
3. The resistance value changes with age
4. A limited range of resistance values
1-62. Which of the following types of resistors
carbon resistor?
1. Rheostat
2. Potentiometer
3. Molded composition
4. Wirewound resistor
1-63. What is the total number of connections on
(a) a rheostat and (b) a potentiometer?
1. (a) Two (b) two
2. (a) Two (b) three
3. (a) Three (b) two
4. (a) Three (b) three
7
1-64. Which, if any, of the following types of
amount of current?
1. Rheostat
2. Potentiometer
3. Wirewound potentiometer
4. None of the above
1-65. A carbon resistor is color-coded orange,
orange, orange. What is the resistance
value of this resistor?
1. 2.2 k!
2. 3.3 k!
3. 33.0 k!
4. 440.0 k!
1-66. What are the allowable limits of ohmic
yellow, gold?
1. 682.5 k! to 617.5 k!
2. 715.0 k! to 585.0 k!
3. 7.98 M! to 7.22 M!
4. 8.36 M! to 6.84 M!
1-67. Of the following, which color of the fifth
chance of failure?
1. Red
2. Brown
3. Yellow
4. Orange
INTENTIONALLY.
THROUGH 1-70, REFER TO FIGURE 1A.
1-68. What is the ohmic value of the resistor?
1. 8!
2. 79!
3. 790!
4. 800!
1-69. What is the specified tolerance of the
resistor?
1. 1%
2. 5%
3. 10%
4. 20%
1-70. What is the specified reliability of the
resistor?
1. 1.0%
2. 0.1%
3. 0.01%
4. 0.001%
8
Textbook assignment: Chapter 2, “Batteries,” pages 2-1 through 2-29. _____________________________________________________________________________________________ 2-1. Which of the following is the purpose of
an electrical cell?
1. To change mechanical energy to electrical energy
2. To change chemical energy to electrical energy
3. To change electrical energy to mechanical energy
4. To change electrical energy to chemical energy
2-2. What are the three basic parts of a cell? 1. Electrodes, electrolyte, container 2. Electrodes, acid, water 3. Anode, cathode, ions 4. Anode, load, depolarizer _______________________________________ IN ANSWERING QUESTIONS 2-3 THROUGH 2-6, SELECT THE PHRASE FROM THE FOLLOWING LIST THAT DESCRIBES THE PART OF A CELL IN THE QUESTION.
A. PARTS OF A CELL
B. DESCRIPTIVE PHRASE
2-3. Electrolyte 1. negative electrode
2-4. Container 2. positive electrode
2-5. Anode 3. solution acting
2-6. Cathode 4. mounting for the electrode
2-7. What term is given to the process that takes place inside a cell?
1. Electromagnetic action 2. Piezoelectric action 3. Electromechanical action 4. Electrochemical action 2-8. With respect to recharging a primary or
secondary cell, of the following statements, which one is correct?
1. The secondary cell can be recharged
2. The primary cell can be recharged by passing current through it in the proper direction
3. The secondary cell can only be recharged by changing the electrodes
4. The primary cell can only be recharged by changing the electrolyte
2-9. What determines the amount of current
that a cell can deliver to the external circuit?
1. The internal resistance of the cell only 2. The resistance of the external load
only 3. The circuit resistance and the internal
resistance of the cell 4. The circuit capacitance and number of
9
2-10. Which of the following actions will lower the internal resistance of a cell?
1. Decreasing the size of the electrodes 2. Increasing the size of the electrodes 3. Increasing the spacing between the
electrodes 4. Increasing the resistance of the
electrolyte 2-11. What causes negative ions to be attracted
to the cathode of a primary cell while the cell is discharging?
1. A negative charge caused by a loss of
electrons 2. A negative charge caused by an
excess of electrons 3. A positive charge caused by a loss of
electrons 4. A positive charge caused by an excess
2-12. What causes hydrogen to be attracted to the anode of a primary cell when the cell is discharging?
1. A negative charge caused by a loss of
electrons 2. A negative charge caused by an
excess of electrons 3. A positive charge caused by a loss of
electrons 4. A positive charge caused by an excess
of electrons 2-13. What causes the cathode to be "eaten
away" in the primary cell while the cell is discharging?
1. The material of the cathode combines
with the negative ions to form a new substance.
2. The material of the cathode dissolves in the electrolyte.
3. The material of the cathode leaves the negative terminal of the cell and goes through the load to the anode.
4. Bacteria in the electrolyte erodes the material in the cathode.
2-14. The primary cell is completely discharged when which of the following conditions exists?
1. The cathode is completely eaten away 2. The active ingredient in the electrolyte
is used up 3. The voltage of the cell is reduced to
zero 4. Each of the above
2-15. In a zinc-carbon primary cell, what is the
function of the carbon electrode? 1. To generate electrons 2. To supply a return path for current 3. To speed electrolysis 4. To collect hydrogen 2-16. The lead-acid cell is an example of which
of the following types of cells? 1. The dry cell 2. The voltaic cell 3. The primary cell 4. The secondary cell 2-17. In a fully charged lead-acid cell, what is
the composition of the anode, cathode, and electrolyte respectively?
1. Zinc, carbon, and water 2. Carbon, lead, sulfuric acid and water 3. Lead peroxide, sponge lead, sulfuric
acid, and water 4. Nickel, cadmium, potassium
10
2-18. Which of the following actions will recharge a secondary cell?
1. Adding more water to the electrolyte 2. Adding more active ingredient to the
electrolyte 3. Connecting the negative terminal of a
4. Connecting the negative terminal of a voltage source to the anode of the cell and the positive terminal of the voltage source to the cathode of the cell
A. Sulfuric acid decreasing B. Sulfuric acid increasing C. Sponge lead decreasing D. Sponge lead increasing E. Lead peroxide decreasing F. Lead peroxide increasing G. Lead sulfate decreasing H. Lead sulfate increasing
IN ANSWERING QUESTIONS 2-19 AND 2-20, REFER TO FIGURE 2A. SELECT THE CORRECT CHEMICAL ACTIONS WITHIN A LEAD-ACID CELL FOR THE CONDITION STATED IN EACH QUESTION. 2-19. The cell is discharging. 1. A, C, E, H 2. A, D, E, G 3. B, C, F, G 4. B, D, F, H
2-20. The cell is charging. 1. A, C, F, H 2. B, C, F, H 3. A, D, F, G 4. B, D, F, G 2-21. When all the lead sulfate in a lead-acid
cell is converted to sulfuric acid, lead peroxide, and sponge lead, what is the condition of the cell?
1. Fully charged 2. Discharged 3. Sulfated 4. Unusable 2-22. Polarization has what effects on an
electrical cell?
1. Decreases internal resistance, thereby increasing the output voltage
2. Decreases internal resistance, thereby decreasing the output voltage
3. Increases internal resistance, thereby increasing the output voltage
4. Increases internal resistance, thereby decreasing the output voltage
2-23. Which of the following methods is used to
control polarization in a cell?
1. Venting the cell 2. Heating the electrolyte 3. Adding mercury to the electrode
material 4. Using an electrolyte that absorbs
oxygen 2-24. Which of the following is caused by local
action in a cell?
1. Shelf life is reduced 2. Hydrogen is generated in large
quantities 3. Impurities rise to the surface of the
electrolyte 4. Mercury coating of the zinc electrode
11
2-25. In a dry cell, what is the consistency of the electrolyte?
1. Solid 2. Liquid 3. Paste 4. Powder 2-26. What serves as the cathode in a common
type of dry cell? 1. Carbon electrode 2. Zinc container 3. Steel cover 4. Nickel terminal 2-27. How should the dry cell be stored to
obtain maximum shelf life? 1. In a dark container 2. In a heated cabinet 3. In a ventilated area 4. In a refrigerated space 2-28. The blotting paper in a dry cell serves
which of the following purposes?
1. Separates the paste from the zinc 2. Permits the electrolyte from the paste
to filter through to the zinc slowly 3. Both 1 and 2 above 4. Keeps the electrolyte dry
2-29. Of the following characteristics, which
one describes the mercury cell?
1. It is physically one of the largest cells 2. It has a very stable output voltage 3. It is designed to be rechargeable 4. It produces a large amount of current
but has a short shelf life 2-30. Which of the following describes the
shorting of a cell?
1. Decreasing the length of a cell 2. Connecting the anode and cathode
together without a load 3. Using the cell below its full potential 4. Providing a recharge voltage that is
2-31. What is/are the advantages(s) of using a manganese-dioxide-alkaline- zinc cell over the zinc-carbon cell?
1. Better voltage stability 2. Longer storage life 3. Operates over a wide temperature
range 4. All the above
2-32. What is the common name for manganese-
dioxide-alkaline-zinc cell? 1. Alkaline cell 2. Long-life cell 3. Moz cell 4. Manganese-dioxide cell 2-33. Which of the following factors should be
considered when selecting a primary cell as a power source?
1. Power requirement 2. Type of electrolyte used 3. Container material 4. All of the above 2-34. Of the following types of cells, which one
is a primary cell? 1. Nickel cadmium 2. Silver zinc 3. Lithium organic 4. Silver cadmium 2-35. Which of the following is/are the
difference(s) in the construction of a NICAD cell as compared to a lead-acid cell?
1. The electrolyte used 2. The material of the anode 3. The material of the cathode 4. All of the above
12
2-36. What is the most common use of a silver- zinc cell?
1. Flashlight batteries 2. Automobile batteries 3. Aircraft storage batteries 4. Emergency equipment batteries 2-37. In addition to the nickel-cadmium and
silver-zinc cells, which of the following cells uses potassium hydroxide as the active ingredient in the electrolyte?
1. Lead-acid cell 2. Silver-cadmium 3. Lithium-inorganic cell 4. Magnesium-manganese dioxide cell 2-38. What is the minimum number of cells
necessary to form a battery? 1. One 2. Two 3. Three 4. Four
IN ANSWERING QUESTIONS 2-39 AND 2-40, REFER TO FIGURE 2B. EACH CELL IS 1.5 VOLTS AND HAS A CAPACITY OF 1/8 AMPERE. 2-39. What type of connection is used to
combine the cells? 1. Series 2. Parallel 3. Series-parallel
2-40. What is the (a) voltage output and (b) current capacity of the circuit?
1. (a) 1.5 volts (b) 1/8 ampere 2. (a) 1.5 volts (b) 5/8 ampere 3. (a) 7.5 volts (b) 1/8 ampere 4. (a) 7.5 volts (b) 5/8 ampere
IN ANSWERING QUESTIONS 2-41 AND 2-42, REFER TO FIGURE 2C. EACH CELL IS 1.5 VOLTS AND HAS A CAPACITY OF 1/8 AMPERE. 2-41. What type of connection is used to
combine the cells? 1. Series 2. Parallel 3. Series-parallel 2-42. What is the (a) voltage output and
(b) current capacity of the circuit? 1. (a) 1.5 volts (b) 1/8 ampere 2. (a) 1.5 volts (b) 5/8 ampere 3. (a) 7.5 volts (b) 1/8 ampere 4. (a) 7.5 volts (b) 5/8 ampere
13
2-43. Which of the following diagrams shows the proper connections for obtaining 6 volts at 1/4 ampere? (Each cell is 1.5 volts and has a capacity of 1/8 amp.)
IN ANSWERING QUESTIONS 2-44 AND 2-45, REFER TO FIGURE 2D. EACH CELL EQUALS 1.5 VOLTS AND HAS A CAPACITY OF 1/8 AMPERE. 2-44. What type of connection is used to
combine the cells? 1. Series 2. Parallel 3. Series-parallel
2-45. What is the (a) voltage output and (b) current capacity of the circuit?
1. (a) 1.5 volts (b) 1.5 amperes 2. (a) 4.5 volts (b) 1/2 ampere 3. (a) 9 volts (b) 1/4 ampere 4. (a) 18 volts (b) 1/8 ampere 2-46. What is the first step in performing
maintenance on a secondary-cell battery?
1. Check the level of the electrolyte 2. Check the technical manual for
3. Check the terminals for cleanliness and good electrical connection
4. Check the battery case for cleanliness and evidence of damage
2-47. When a hydrometer is used to check the
specific gravity of the electrolyte in a battery, to what level should the electrolyte be drawn?
1. Enough to just wet the float 2. Enough so the float will rise without
entering the suction bulb 3. Enough so the top one-third of the
float will rise into the suction bulb 4. Enough so the float is completely
covered by the electrolyte 2-48. To flush a hydrometer, which of the
following liquids should be used? 1. Sulfuric acid 2. Salt water 3. Fresh water 4. A solution of baking soda and water 2-49. If the electrolyte level in a battery is low,
what should be added to the electrolyte to bring it to the proper level?
1. Tap water 2. Sulfuric acid 3. Potassium hydroxide 4. Distilled water
14
2-50. Which one of the following safety precautions for batteries is NOT correct?
1. Terminals should be electrically
2. Care should be taken to prevent the spilling of electrolyte
3. Smoking, open flames, and electrical sparks are prohibited around charging batteries
4. Protective clothing, such as rubber apron, rubber gloves, and face shield, should be worn when working on batteries
2-51. If electrolyte comes in contact with the
skin, what first aid treatment should be given immediately to the affected area?
1. Cover with petroleum jelly 2. Wrap with a sterile bandage 3. Apply an antiseptic lotion 4. Flush with fresh water 2-52. A battery with a capacity of 600
ampere-hours should provide 3 amperes for a maximum of how many hours?
1. 100 hr 2. 200 hr 3. 300 hr 4. 600 hr 2-53. A battery is rated according to a 20-hour
rate of discharge at 300 ampere-hours. Which of the following currents is the maximum current that will allow the battery to deliver its rated capacity?
1. 15 amperes 2. 20 amperes 3. 25 amperes 4. 30 amperes
2-54. Which of the following types of routine charges follows the nameplate data in restoring a battery to its charged condition during the ordinary cycle of operation?
1. Initial 2. Floating 3. Normal 4. Fast THIS SPACE LEFT BLANK INTENTIONALLY.
15
_______________________________________ IN ANSWERING QUESTIONS 2-55 THROUGH 2-58, MATCH THE DESCRIPTION GIVEN IN THE FOLLOWING LIST WITH THE TYPE OF BATTERY CHARGE IN THE QUESTION.
A. TYPE OF CHARGE
B. DESCRIPTION
2-55. Initial charge 1. Used in emergency only
2-56. Equalizing
charge 2. Used periodically as
2-57. Floating
charge 3. Used to keep a battery
2-58. Fast charge 4. Used after electrolyte
_______________________________________ 2-59. If violent gassing occurs during the
charging of a battery, which of the following actions should be taken?
1. Increase the room ventilation 2. Decrease the room temperature 3. Increase the charging rate 4. Decrease the charging rate 2-60. If a battery is being charged at the proper
rate, which, if any of the following types of gassing should occur?
1. Steady gassing 2. Intermittent gassing 3. Violent gassing 4. None
16
Textbook assignment: Chapter 3, Direct Current, pages 3-1 through 3-126.
THROUGH 3-3, REFER TO FIGURE 3A.
3-1. What parts of the circuit represent the
(a) source and (b) load?
1. (a) Es (b) S1
2. (a) Es (b) R1
3. (a) S1 (b) R1
4. (a) S1 (b) Es
3-2. Which of the following terms describes
the circuit condition?
1. Partially shorted
2. Partially open
3. Shorted
4. Open
3-3. Which of the following terms describes
the figure 3A?
1. Parts layout
2. Exploded view
3. Wiring diagram
4. Schematic diagram
3-4. If circuit voltage is held constant, circuit
resistance (a) increases, and (b) decreases?
1. (a) Increase (b) decrease
2. (a) Increase (b) increase
3. (a) Decrease (b) decrease
4. (a) Decrease (b) increase
3-5. If circuit resistance is held constant,
(b) decreases?
1. (a) Increase (b) decrease
2. (a) Increase (b) increase
3. (a) Decrease (b) decrease
4. (a) Decrease (b) increase
3-6. According to Ohm's law, what formula
if resistance and current value are known?
17
REFER TO FIGURE 3B.
3-7. If the current is 15 amperes, what is the
value of the voltage?
1. 50 V
2. 75 V
3. 100 V
4. 150 V
3-8. If the voltage is 200 volts, what is the
value of the current?
1. 10 A
2. 20 A
3. 30 A
4. 40 A
3-9. Which of the following terms applies to
motion?
1. Power
2. Energy
3. Inertia
4. Each of the above
3-10. Which of the following circuit quantities
the other circuit quantities?
1. Voltage
2. Current
3. Resistance
4. Each of the above
3-11. Which of the following is a correct
electrical circuit?
3-12. What is the current in a circuit with
of power?
1. 10 A
2. 15 A
3. 3 A
4. 9 A
3-13. What is the total power used by a 15-ohm
resistor with 4 amps of current?
1. 60 W
2. 240 W
3. 360 W
4. 900 W
3-14. What type of resistor should be used in
question 3-13?
1. Carbon
2. Wirewound
3. Precision
4. Composition
18
3-15. How much total energy is converted by a
l-horsepower motor in 10 hours?
1. 7.46 kWh
2. 8.32 kWh
3. 8.59 kWh
4. 9.32 kWh
3-16. If the energy used by the motor in
question 3-15 is 9.5 kWh, what is the
efficiency of the motor?
1. .981
2. .904
3. .876
4. .785
THROUGH 3-23, REFER TO FIGURE 3C.
3-17. What is the total circuit resistance (R)?
1. 20!
2. 60!
3. 180!
4. 240!
3-18. If the circuit current is 3 amps, what is the
source voltage (Es)?
1. 60 V
2. 180 V
3. 540 V
4. 720 V
3-19. What is the total voltage dropped by each
resistor in question 3-18?
1. 20 V
2. 60 V
3. 180 V
4. 540 V
3-20. If the current decreases to 2 amps, what is
the total voltage drop across each resistor?
1. 120 V
2. 230 V
3. 310 V
4. 400 V
3-21. What would have to be done to the circuit
to cause the current to decrease to 2 amps?
1. The source voltage would have to be
2. The source voltage would have to be
3. The resistance of R1 would have to be
4. One of the resistors would have to be
3-22. If the circuit current is 2 amps, what is the
total power used by each resistor?
1. 240 W
2. 460 W
3. 620 W
4. 800 W
3-23. What is the total power used in the circuit
if Es = 360 V?
1. 720 W
2. 1380 W
3. 1860 W
4. 2400 W
19
3-24. When Kirchoff's voltage law is used to
the resistor that the current enters?
1. Ground
2. Neutral
3. Negative
4. Positive
3-26, REFER TO FIGURE 3D.
3-25. What is the effective source voltage?
1. 15 V
2. 25 V
3. 50 V
4. 75 V
3-26. What is the total amount and direction of
current through R 3?
1. 1.0 A from Y to X
2. 1.0 A from X to Y
3. .33 A from Y to X
4. .33 A from X to Y
3-27. Which of the following terms applies to a
path for current?
1. Open
2. Short
3. Closed
4. Grounded
3-28. A circuit in which the resistance is almost
following terms?
1. Open
2. Short
3. Closed
4. Broken
INTENTIONALLY.
20
THROUGH 3-32, REFER TO FIGURE 3E.
3-29. If R2 has a short circuit, what will most
likely happen to the circuit?
1. R1 will be destroyed
2. Es will increase
3. V will indicate O volts
4. S1 will automatically open
3-30. What is the total voltage drop across Ri
when the switch is closed?
1. 2.5 V
2. 6.5 V
3. 97.5 V
4. 100.0 V
3-31. What will the meter indicate with (a) S1
open, and (b) S1 closed?
1. (a) 100 V (b) 100 V
2. (a) 97.5 V (b) 100 V
3. (a) 100 V (b) 97.5 V
4. (a) 97.5 V (b) 97.5 V
3-32. To achieve maximum power transfer in
conditions must be met?
1. Ri = RL
2. Is = IL
3. Es = EL
4. Ks = KL
3-33. Maximum power is transferred from a
compared to the source resistance?
1. Equal
2. Twice
3. One-half
4. Several times
3-34. When maximum power is transferred from
of power transfer?
1. 5%
2. 25%
3. 50%
4. 95%
3-35. A circuit consists of three resistors
connected in parallel. R1 = 30 ohms,
R2 = 15 ohms, and R 3 = 10 ohms. If the
the total source voltage?
1. 20 V
2. 60 V
3. 120 V
4. 220 V
3-36. What is the relationship of total current to
series circuit, and (b) a parallel circuit?
1. (a) Divides (b) divides
2. (a) Divides (b) equals
3. (a) Equals (b) equals
4. (a) Equals (b) divides
21
3-37. If a current has a negative polarity when
current?
1. It is from a battery
2. It is from a generator
3. It is entering a junction
4. It is leaving a junction
3-38. Three equal resistors are connected in
value of 300 ohms. What is the equivalent
resistance of the circuit?
1. 100!
2. 150!
3. 600!
4. 900!
3-39. Three resistors with ohmic values of
connected in parallel. What is the
equivalent resistance of the circuit?
1. 10!
2. 20!
3. 30!
4. 40!
3-40. Two resistors with ohmic values of
parallel. What is the equivalent resistance
of the circuit?
1. 10!
2. 20!
3. 30!
4. 40!
3-41. Which of the following terms describes a
circuit?
1. Equal resistor
2. Phantom resistor
3. Schematic resistor
4. Equivalent resistor
INTENTIONALLY.
22
THROUGH 3-46, REFER TO FIGURE 3F.
3-42. What is the value of Es?
1. 336 V
2. 300 V
3. 240 V
4. 120 V
3-43. What is the value of current through R2?
1.  What is the approximate value of total
resistance?
1. 8!
2. 37!
3. 112!
4. 257!
3-45. What is the value of total power?
1. 1.2 kW
2. 1.5 kW
3. 1.8 kW
4. 2.0 kW
3-46. What is the total power consumed by R 3?
1. 108 W
2. 240 W
3. 360 W
4. 1200 W
THROUGH 3-49, REFER TO FIGURE 3G.
3-47. What is the value of the total resistance?
1. 3.6!
2. 15!
3. 34!
4. 40!
3-48. What is the total power used in the circuit?
1. 22.5 W
2. 26.5 W
3. 60.0 W
4. 250.0 W
3-49. What is the total voltage drop across R 3?
1. 8 V
2. 12 V
3. 18 V
4. 30 V
23
3-51, REFER TO FIGURE 3H.
3-50. What is the value of total resistance?
1. 5!
2. 8!
3. 13!
4. 15!
3-51. If an equivalent resistor is used to
across this resistor?
1. 8V
2. 26V
3. 52V
4. 60V
3-52. If an open occurs in a series portion of a
resistance, and (b) total current?
1. (a) Decreases to zero
2. (a) Decreases to zero
3. (a) Becomes infinite
4. (a) Becomes infinite
3-53. If an open occurs in a parallel branch of a
resistance, and (b) total current?
1. (a) Increases (b) decreases
2. (a) Increases (b) increases
3. (a) Decreases (b) decreases
4. (a) Decreases (b) increases
3-54. If a short circuit occurs in a series portion
resistance, and (b) total current?
1. (a) Increases (b) decreases
2. (a) Increases (b) increases
3. (a) Decreases (b) decreases
4. (a) Decreases (b) increases
3-55. If a short circuit occurs in a parallel
(a) total resistance, and (b) total current?
1. (a) Increases (b) decreases
2. (a) Increases (b) increases
3. (a) Decreases (b) decreases
4. (a) Decreases (b) increases
3-56. If one branch of a parallel network shorts,
branches?
1. An amount determined by the
2. All
3. One-half
4. None
3-57. Which of the following circuit quantities
voltage divider?
1. The current of the source
2. The voltage of the source
3. The current requirement of the load
4. The voltage requirement of the load
24
OF CURRENT. THE SOURCE VOLTAGE IS
250 VOLTS. (HINT: DRAW THE CIRCUIT.)
3-58. What should be the value of the bleeder
current?
1. 3 A
2. 300 mA
3. 30 mA
4. 3 mA
3-59. What should be the ohmic value of the
bleeder resistor?
1. 50
2. 500
3. 5 k
4. 50 k
3-60. What is the value of total current?
1. 303 mA
2. 330 mA
3. 600 mA
4. 3300 mA
THROUGH 3-66, REFER TO FIGURE 3I.
3-61. Why must the value of R1 be calculated
first?
1. For convenience
2. The current through R2 depends on the
3. The voltage drop across R1depends on
4. In any circuit, values for resistors
3-62. How is the current through R2 calculated?
1. By adding IR1 and the current
2. By adding the current requirements of
3. By subtracting the current requirement
4. By subtracting the current requirement
25
3-63. How is the voltage drop across R2
calculated?
1. By adding the voltage requirements of
2. By subtracting the voltage drops
3. By subtracting the voltage
4. By subtracting the voltage
3-64. What is the minimum wattage rating
required for R5?
1. 1 W
2. 2 W
3. 1/2 W
4. 1/4 W
3-65. What is the total power supplied by the
source?
1. 3.765 W
2. 7.965 W
3. 8.209 W
4. 8.965 W
3-66. What is the purpose of using the series-
R5 in place of a single resistor?
1. It provides the desired resistance with
2. It provides the close tolerance
3. It is more reliable than the use of a
4. It costs less by using three resistors of
3-67. A single voltage divider provides both
1. ground between two of the dividing
2. ground to the positive terminal of the
3. ground to the negative terminal of the
4. ground to the input of all loads
3-68. Which of the following voltages are
considered dangerous?
1. Voltages above 115 volts only
2. Voltages above 230 volts only
3. Voltages above 450 volts only
4. All voltages
3-69. If you discover a possible malfunction in
actions should be taken?
1. Attempt repairs yourself
2. Report the malfunction to a qualified
3. Ignore the malfunction unless you
4. Secure the circuit immediately by
3-70. If a person has stopped breathing and
should perform CPR?
1. Medical personnel only
2. The first person on the scene
3. Emergency Medical Technicians only
4. Trained, qualified personnel only