A long solenoid with 15 turns per cm has a small loop of area 2.0 ${{cm}^{2}}$ placed inside, normal to the axis of solenoid. If the current carried by the solenoid changes steadily from 2 A to 4 A in 0.1 s, what is the induced voltage in the loop, while the current is changing?

Here, number of turns per unit length,

n= N/l = 15 turns/cm=1500 turns/m

A = 20 {{cm}^{2}} = 2 x ${{10}^{-4}}$${{m}^{2}}
dI/dt = 4-2/0.1 or dI/dt = 20 A{{s}^{-1}}$