A 10 cm conducting strip lies on a U-shaped wire and is attached to a spring of spring constant 0.5 N m⁻¹. The system is in a uniform magnetic field 0.1 T as shown. If the strip is displaced and released, the number of oscillations before its amplitude falls by a factor e is closest to:

Question

G1 Physics · Accepted Answer

Electromagnetic damping has effective constant b=B²ℓ²/R. Using B=0.1 T, ℓ=0.10 m, R=10 Ω and m=0.05 kg, the e-fold decay time combined with the oscillation frequency gives about 5000 oscillations. Hence option B.