91Ó°ÊÓ

Magnetic flux is given by

$\mathit{ϕ}\mathbf{=}\stackrel{\mathbf{→}}{\mathbf{B}}\mathbf{.}\stackrel{\mathbf{→}}{\mathbf{A}}$

Where$\stackrel{\mathbf{→}}{\mathbf{B}}$ is the magnetic field and$\stackrel{\mathbf{→}}{\mathbf{A}}$is the area vector

Faraday’s law states that The induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

$\mathbf{emf}\mathbf{=}\mathbf{-}\mathbf{N}\frac{\mathbf{∆}\mathbf{ϕ}}{\mathbf{∆}\mathbf{t}}$

Replacing the change of flux into faraday’s law we get

$\mathrm{emf}=-\mathrm{N}\frac{∆\left(\mathrm{BA}\right)}{∆\mathrm{t}}$

Replace N=1 and since only the magnetic field changes

$\mathrm{emf}=\mathrm{A}\frac{\mathrm{dB}}{\mathrm{dt}}$

Hence greater the area , greater is the induced emf.

So emf at the periphery of the dashed lines has the greatest emd since it has the largest area.

Therefore, the right choice is b