A coil having an area A₀ is placed in a magnetic field which changes from B₀ to 4B₀ in time interval t. The emf induced in the coil will be. 
 

Given data:

Area of the coil A=A₀

Magnetic field changes from B₀ to 4B₀

Concept used: Induced EMF

Detailed solution:

$\text{Induced e.m.f. }=\frac{\text{d}\varphi }{\text{dt}}$

$=\frac{\text{d}\left(\text{BA}\right)}{\text{dt}}={\text{A}}_0\frac{\text{dB}}{\text{dt}}$

$EMF={\text{A}}_0\left(\frac{4 {\text{B}}_0-{\text{B}}_0}{\text{t}}\right)$

$=\frac{3 {\text{A}}_0 {\text{B}}_0}{t}$