The formula for induced e.m.f. in a coil due to change in magnetic flux through the coil is (here A = area of the coil, B = magnetic field) 

• A

  $\mathrm{e}=-\mathrm{A}\cdot \frac{\mathrm{dB}}{\mathrm{dt}}$

• B

  $\mathrm{e}=-\mathrm{B}\cdot \frac{\mathrm{dA}}{\mathrm{dt}}$

• C

  $\mathrm{e}=-\frac{\mathrm{d}}{\mathrm{dt}}(\mathrm{A}\cdot \mathrm{B})$

• D

  $\mathrm{e}=-\frac{\mathrm{d}}{\mathrm{dt}}(\mathrm{A}\times \mathrm{B})$