2.1 Two lamps are connected in series to a 120-V line. The voltage across one lamp is 70 V. What is the voltage across the second lamp? (2.1Ans)
2.2 Eight lamps of the same size are connected in series to a 120-V circuit. What is the voltage across each lamp? (2.2Ans)
2.3 Three lamps of equal size are connected in parallel to a lighting circuit. Each lamp draws a current of 1.5 A. What is the total line current? (2.3Ans)
2.4 Twenty lamps of equal size are connected in parallel to a 120-V lighting circuit. If the total current drawn by the 20 lamps is 15 A, what is the current through each lamp? If the lamps are reconnected in series in another circuit, so that the current through one of the lamps is 1 A, what will be the current through the other 19 lamps? (2.4Ans)
2.5 A 220-ohm lamp is connected to a 110-V circuit. What current does it take? (2.5Ans)
2.6 The field resistance of a shunt motor is 93 ohms. What will be the field current if 240 V is applied to the field terminals? (2.6Ans)
2.7 An accidental short circuit is made on a 240-V circuit by placing a 0.15 Ohm resistance across the line. What will be the momentary short-circuit current? (2.7Ans)
2.8 A telephone receiver has a resistance of 1200 Ohm. If a current of 0.02 A is to flow through the receiver, what voltage must be used? (2.8Ans)
2.9 What is the voltage drop across a rheostat if its resistance is 5 Ohm and the current through it is 26 A? (2.9Ans)
2.10 Find the voltage drop across an electric furnace that has a resistance of 5 Ohm and draws 43 A. (2.10Ans)
2.11 The voltage across the terminals of a motor field is 220 V, and the field current is 1 A. What is the field-circuit resistance? (2.11Ans)
2.12 A relay coil draws a current of 0.03 A when connected to a 12-V battery. What is its resistance? (2.12Ans)
2.13 Find the combined resistance of a 5 Ohm rheostat in series with a 56 Ohm shunt field. (2.13Ans)
2.14 What is the total resistance of a string of eight Christmas-tree lights connected in series, if the resistance of each lamp is 30 Ohms? (2.14Ans)
2.15 How much voltage is required to cause a current of 0.4 A to flow through a 70-Ohm, a 90-Ohm, and a 120-Ohm lamp all connected in series? (2.15Ans)
2.16 Three lamps are connected in series across a 120-V supply and take a current of 1.25 A. If the resistance of two of the lamps is 25 Ohms each, what is the resistance of the third? (2.16Ans)
2.17 How much resistance must be added in series with a 60-Ohm generator field if the field current desired is 2 A and the voltage applied to the field circuit is 230 V? (2.17Ans)
2.18 A certain series street-lighting system of 60 lamps operates at a constant current of 6.6 A. How much voltage must be applied in the circuit if each lamp has a resistance of 5 Ohm and the total line resistance is 10 Ohm? (2.18Ans)
2.19 Four lamps of equal resistance are connected in parallel across a 120-V circuit. If the total current supplied the lamps is 3 A, what is is the resistance of each lamp? (2.19Ans)
2.20 Three resistances A, B, and C are connected in parallel across a 120-V line. If A = 10 Ohm, B = 30 Ohm, and C = 40 Ohm, find (a) the voltage across each resistance, (b) the current through each resistance, (c) the total line current, and (d) the combined resistance of the circuit. (2.20Ans)
2.21 The combined resistance of two resistors connected in parallel is 8 Ohms. The resistance of one resistor is 14 Ohms. What would be their combined resistance if they were reconnected in series? (2.21Ans)
2.22 A trolley wire is paralleled for 3 miles by a heavy copper cable. The trolley-wire resistance is 0.3 Ohms per mile, and the cable resistance is 0.10 Ohms per mile. When the sum of the two currents through the two lines is 150 A, find the current in each conductor. (2.22Ans)
2.23 A parallel circuit has three branches of 12, 4, and 16 Ohm, respectively. If a current of 4 A flows in the branch containing 12 Ohm, what current will flow in each of the others? (2.23Ans)
2.24 Three resistances of 3, 4, and 6 Ohm are connected in parallel. In series with the group is an unknown resistance R. When the circuit is connected to a 12-V battery, a current of 4 A flows. What is the resistance of R? (2.24Ans)
2.25 A resistance of 12 Ohm is connected in parallel with a series circuit of a 15 Ohm and a 5 Ohm resistance. A 40 Ohm resistance is connected in series with the combination. What is the resistance of the entire circuit? (2.25Ans)
2.26 Three resistances of 4, 8, and 10 Ohm are connected so that each resistance forms the side of a triangle. Point A is the connection between the 4-and 8-Ohm sides; point B, between the 8-and 10-Ohm sides; and point C, between the 4-and 10-Ohm sides. Find the resistance between points A and B, B and C, and C and A. (2.26Ans)
2.27 Four resistors of 6 Ohm each form the sides of a diamond. A fifth resistor of 10 Ohm forms the long diagonal of the diamond. What is the resistance of the combination between the ends of the long diagonal? What is the resistance between one end of the long diagonal and one end of the short diagonal? (2.27Ans)
2.28 A dc motor is supplied by a dc generator. Each line connecting the two machines has a resistance of 0.15 Ohm. What is the terminal voltage across the motor when the motor current is 50 A and the generator terminal voltage is 230 V? (2.28Ans)
2.29 A dc motor is located 2000 ft from a dc generator. The motor requires 30 A to operate a given load. The generator voltage is 220 V. Each line connecting the generator and motor is No. 0 cable, which has a resistance of 0.1 0 per 1000 ft. Find the voltage at the motor. (2.29Ans)
2.30 A 240-V generator supplies 10 A to each of two motors connected in parallel. The resistance of each line wire between the generator and the first motor is 0.3 Ohm, and the resistance of each line wire between the first and second motor is 0.4 Ohm. What is the voltage across each motor? (2.30Ans)
2.31 Each wire of a two-wire distribution circuit has a resistance of 0.2 Ohm per 1000 ft. Connected to this circuit at a point 500 ft from the generator is a motor that requires a current of 15 A and has a terminal voltage of 230 V. A second motor that requires 10 A is located on the same circuit but 750 ft from the generator. (a) What is the voltage at the second motor? (b) What is the generator voltage? (2.31Ans)
2.32 The voltage drop across an electric heater is 225 V. If the voltage at the source is 230 V and the heater draws 15 A, what is the resistance of each connecting line wire? (2.32Ans)
2.33 If each lamp in Fig. 2-20 requires a current of 1 A, find (a) the current and its direction in each of the three lines, (b) the IR drop in each line, and (c) the voltages V1 and V2.
(2.33Ans)
2.34 Repeat the preceding problem if one lamp in the upper bank of lamps burns out. (2.34Ans)
