### ANSWER KEY: OHM’S LAW EXERCISE3

1. Suppose a dc circuit contains three resistances R1 = 22 ohms, R2 = 47 ohms, and R3 = 68 ohms across a battery that supplies a voltage of E = 3.0 V. Find the power dissipated by each resistance.

P1 = 9.0/22 =
0.4091 W, P2 = 9.0/47 = 0.1915 W, and P3 = 9.0/68 = 0.1324 W. These should be rounded off to
P1 = 0.41 W, P2 = 0.19 W, and P3 = 0.13 W

2. Suppose we have a series circuit with a supply of 150 V and three resistances: R1 = 330 ohms, R2 = 680 ohms , and R3 = 910 ohms. What is the power dissipated by R2?

Round this off to three significant digits, because that’s all we have in the data,
to obtain 4.15 W.

3. Suppose three resistors are in parallel across a battery that supplies E = 12 V. The resistances are R1 = 22 ohms, R2 = 47 ohms, and R3 = 68 ohms. These resistances carry currents I1, I2, and I3, respectively. What is the current, I3, through R3?

I3 = E/R3 = 12/68 = 0.18 A.

4. In the scenario shown by Fig. 1, what is the voltage across the combination of R3 and R4?

Ans. 5 V