Electricity - Basic Navy Training Courses
NAVPERS 10548
Here is the "Electrician's Mate 3 - Navy Training Courses" (NAVPERS 10548) in its entirety (or will be eventually). It should provide one of the Internet's best resources for people seeking a basic electricity course - complete with examples worked out. See copyright. See Table of Contents.
¶ U.S. GOVERNMENT PRINTING OFFICE; 1949
CHAPTER 1 QUIZ
ELECTRICAL CURRENTS AND CIRCUITS - OHM'S LAW ELECTRICITY
1. The unit of electrical pressure is the _____________.
2. The unit of electrical current is the _____________.
3. The unit of electrical resistance is the _____________.
4. The current in a circuit is
(a) _____________ proportional to the applied voltage.
(b) _____________ proportional to the resistance.
5. The relation between current, voltage and resistance in a circuit is expressed
by the equation
Amperes _____________.
6. If a generator supplies 60 volts across a resistor and a current of 10 amperes
flows through the circuit, what is the ohmic value of the resistor?
7. A generator is supplying 120 volts to a circuit which comprises two resistances,
6 ohms and 4 ohms, in series. What is the current flowing in the circuit?
8. What voltage must a generator have to produce a current of 6 amperes through
resistances of 2 ohms, 3 ohms, and 5 ohms connected in series?
9. Four resistors, of 8 ohms, 6 ohms, 2 ohms and one of unknown resistance, are
connected in series. A generator supplies 120 volts across this circuit. The IR-drop
across the 6-ohm resistance is 36 volts.
(a) What current is flowing in the circuit?
(b) What is the total circuit resistance? (c) What ohmic value has the unknown resistor?
10. A generator supplies 100 volts to 3 resistors in series, whose resistances are 2 ohms,
3 ohms and 5 ohms. (a) What current flows in the circuit? (b) What is the current in
each resistor?
11. Find the current that would flow in a circuit of 6 ohms and 8 ohms connected in series,
if 140 volts were impressed on the circuit.
12. A generator furnishes 100 volts to a group of 3 resistors connected in parallel. One
resistor is 7 ohms, another 2 ohms, and the third 1 ohm. (a) What current flows in each
resistor? (b) What is the total current flowing in the circuit? (c) What is the equivalent
resistance of all 3 resistors in parallel?
13. A current of 10 amperes flows in a circuit containing 2 resistances in parallel, one
12 ohms and the other 6 ohms. What is the voltage impressed on the circuit?
14. A generator is supplying 10 amperes to a 5-ohm resistor and an unknown resistor in
parallel. If 8 amperes flows through the 5-ohm resistor, what is the ohmic value of the
unknown resistor?
15. Four resistors are connected in parallel. One is 12 ohms, one is 4 ohms, and the other
two are unknown. The current through one unknown resistor is 12 amperes and
through the other unknown 20 amperes when this combination is put across a 120-volt
generator.
(a) What is the total current the generator supplies to the circuit
(b) What is the total power consumed in the circuit?
(c). How much power is used up in each resistor?
16. A generator supplies 150 volts to 3 resistances in parallel. One resistor is 50 ohms, one
75 ohms, and the third is un-known.
(a) If 5 amperes flows through the unknown resistor, what is its resistance?
(b) How much power is expended in each resistor?
(c) How much power is taken by the whole circuit?
17. A generator expends 2,880 watts when supplying a current of 12 amperes to a circuit
consisting of 3 resistances in parallel. One is 60 ohms, another 40 ohms, and the third
unknown. What is the ohmic value of the unknown resistance?
18. A 35-ohm resistor is in series with a parallel group which contains a 50-ohm resistor, a
30-ohm resistor and an unknown resistor. If the total resistance of the circuit is 50 ohms,
what is the ohmic value of the unknown resistor?
19. An unknown resistor is placed in series with two other resistances connected in parallel.
One is 5 ohms, the other one is 20 ohms. This combination of three resistances is in
parallel with one of 50 ohms. If 120 volts is impressed on the circuit and 10 amperes
flows, what is the ohmic value of the unknown resistor?
20. Three groups of resistances are connected in series. The first group contains 20 ohms
and 30 ohms in parallel. The second group contains 6 ohms and an unknown in parallel.
The third group contains 40 ohms and 60 ohms in parallel. If 120 volts is impressed on
the circuit and 3 amperes flow, what is the ohmic value of the unknown resistor?
21. What voltage must a generator have in order to force 20 amperes through a 2-ohm
resistor in series with a parallel group of two others having resistances of 3 ohms and
6 ohms?
22. How much power is expended by a generator that furnishes 130 volts to the following
three groups of resistances connected in series? The first group contains 5 ohms and
20 ohms in parallel. The second group contains a 6-ohm resistor. The third group
contains 4 ohms and 12 ohms in parallel.
23. A generator supplies 120 volts to a lighting circuit. A group of lamps connected in parallel
across the line, nearest the generator, contains two lamps in parallel. A second group
also across the line contains three lamps in parallel. The resistance of each side of the
line from the generator to the first group of lamps is 0.4 ohm. The resistance of each side
of the line between the first group of lamps and the second group is 0.5 ohm. Find the
voltage across each group of lamps if each lamp draws 1 ampere.
24. Fill in the blanks below with the appropriate word to make each sentence a true
statement.
(a) The electrical energy used up in forcing a current through a conductor is
transformed into _____________.
(b) The electrical energy used up each second in forcing electrons through a
conductor depends on the _____________ of the conductor.
(c) The electrical energy used up each second in forcing electrons through a conductor
depends on the square of the _____________.
(d) A slight overload will produce a _____________ increase in heating.
25. How does overheating of a conductor affect the insulation around it?
CHAPTER 1 ANSWERS
ELECTRICAL CURRENTS AND CIRCUITS - OHM'S LAW ELECTRICITY
1. volt
2. ampere
3. ohm
4. (a) directly
(b) inversely
5. volts/ohms
6. 6 ohms
7. 12 amperes
8. 60 volts
9. (a) I = 6 amperes
(b) Rt = 20 ohms
(c) Rx = 20 ohms
10. (a) I = 10 amperes
(b) I = 10 amperes
11. I = 10 amperes
12. (a) IR7 = 14.28
IR2 = 50.00
IR1 = 100.00
(b) IT = 164.28 amperes
(c) RT = 100/164.3 = 0.608 ohms
13. E = 40 volts
14. R = 20 ohms
15. (a) IT = 72 amperes
(b) PT = 8640 watts
(c) PR12 = 1200 watts
PR4 = 3600 watts
PI12 = 1440 watts
PI20 = 2400 watts
16. (a) Rx = 30 ohms
(b) Px = 750 watts
P50 = 450 watts
P75 = 300 watts
(c) PT = 1500 watts
17. Rx = 120 ohms
18. Rx = 75 ohms
19. Rx = 11.80 ohms
20. R = 12 ohms
21. E = 80 volts
22. P = 1300 watts
23. Across 2-lamp group, E = 116 volts
Across 3-lamp group, E = 113 volts
24. (a) heat
(b) resistance
(c) current
(d) great
25. Overheating chars and breaks down the insulation