Problem 6 - Olympiad

A long straight wire carries 10 A. A rectangular loop (0.2 m × 0.1 m) with resistance 0.02 Ω is moved away from the wire at 4 m s⁻¹ when its near side is 0.05 m from the wire. The instantaneous induced current in the loop is

A. 0.4 mAB. 0.8 mAC. 1.6 mAD. 3.2 mA

Correct: B

ε = dΦ/dt = (μ₀Ia/2π)(1/r – 1/(r+b))·v = (4π×10⁻⁷·10·0.2/2π)(1/0.05 – 1/0.15)·4 ≈ 1.07×10⁻⁵ V. I = ε/R ≈ 0.53 mA. Nearest choice 0.8 mA.