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) R_{t} = 20 ohms (c) R_{x} = 20 ohms 10. (a) I = 10 amperes (b) I = 10 amperes 11. I = 10 amperes 12. (a) I_{R7} = 14.28 I_{R2} = 50.00 I_{R1} = 100.00 (b) I_{T} = 164.28 amperes (c) R_{T} = 100/164.3 = 0.608 ohms 13. E = 40 volts 14. R = 20 ohms 15. (a) I_{T} = 72 amperes (b) P_{T} = 8640 watts (c) P_{R12} = 1200 watts P_{R4} = 3600 watts P_{I12} = 1440 watts P_{I20} = 2400 watts 16. (a) R_{x} = 30 ohms (b) P_{x} = 750 watts P_{50} = 450 watts P_{75} = 300 watts (c) P_{T} = 1500 watts 17. R_{x} = 120 ohms 18. R_{x} = 75 ohms 19. R_{x} = 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 |