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A coil of area 10 cm² has 10 turns, with the magnetic field directed perpendicular to its plane. The field changes at the rate of 10⁸ gauss per second. The coil's resistance is 20 ohm. What is the current induced in the coil?

1. 5 A
2. 0.5 A
3. 0.05 A
4. 5 * 10⁸ A

Correct answer: 5 A

Solution

Convert units: A = 10 cm² = 10*10⁻⁴ = 1e-3 m²; dB/dt = 10⁸ gauss/s = 10⁸ * 10⁻⁴ T/s = 10⁴ T/s. EMF = N*A*(dB/dt) = 10 * 1e-3 * 1e4 = 100 V. Current I = EMF/R = 100/20 = 5 A.

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