Question

One thousand watts of electric power are transmitted to a device by means of two wires, each of which has a resistance of 2 ohms. If the resulting potential difference across the device is 100 volts, the potential difference across the source supplying the power is: A. 20 V B. 40 V C. 100 V D. 140 V E. 500 V

Answer 1

One thousand watts of electric power are transmitted to a device by means of a series of two wires, each of which has a resistance of 2 ohms. If the resulting potential difference across the device is 100V the potential difference across the source supplying the power is:

(A)20 V
(B)40 V
(C)100 V
(D)140 V
(E)500 V

In the answer key the answer is (D) and the method used is:

P=VI
I = (P/V) = (1000/100) = 10 A 
IR drop = IR = 20V
100 + 20 + 20 = 140 V

Answer 2

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