Question

A rectangular wire frame, shown below, is placed in a uniform magnetic field directed upward and normal to the plane of the paper. The part AB is connected to a spring. The spring is stretched and released when the wire AB has come to the position A′ B′ (t = 0) How would the induced emf vary with time? Neglect damping.

Answer

When the spring is stretched and released, the wire AB will execute simple harmonic (sinusoidal) motion, so induced emf will vary periodically. At t = 0, wire is at the extreme position. $\text{v}=0.$ $\text{v}=\text{A}\omega\sin\omega\text{t}$ Induced emf $\varepsilon = \text{Bvl}$ $=\text{BA}\omega\text{l}\sin\omega\text{t}$ Where A = BB′= AA′ is the amplitude of motion and ω is angular frequency.

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