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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. How much voltage is required to produce a current of 1 ampere in the rods?

1. 0.117 V
2. 0.00145 V
3. 0.0145 V
4. 1.7 × 10⁻⁶ V

Correct answer: 0.117 V

Solution

The resistance of each rod is calculated using R = ρL/A. For copper, R₁ = (1.7 × 10⁻⁶ × 100) / 0.01 = 0.017 Ω. For iron, R₂ = (10⁻⁵ × 100) / 0.01 = 0.1 Ω. Total resistance R = R₁ + R₂ = 0.117 Ω. Voltage V = IR = 1 × 0.117 = 0.117 V.

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