Two rods are joined end to end, as shown. Both have a cross-sectional area of 0.01 cm2. Each is 1 meter long. One rod is of copper with a resistivity of 1.7 10-6 ohm-centimeter, the other is of iron with a resistivity of 10-5 ohm-centimeter. [figure] How much voltage is required to produce a current of 1 ampere in the rods?
- 0.00145 V
- 0.0145 V
- 1.7 10-6 V
- 0.117 V
Answer
(4) 0.117 V
Solution
R = lA, with l = 1 m = 100 cm, A = 0.01 cm2
RCu = 1.7 10-6 1000.01 = 1.7 10-2
RFe = 10-5 1000.01 = 10-1
The rods are in series:
R = 0.017 + 0.1 = 0.117
∴ V = IR = 1 0.117 = 0.117 V
Answer: (4)