The current in a solenoid of 240 turns, having a length of 12 cm and a radius of 2 cm, changes at a rate of 0.8 A s–1. Find the emf induced in it.
Given:
Number of turns(n) = 240
Length of solenoid(l) = 12 cm = 0.12 m
Radius(r) = 2 cm = 0.02 m
Rate of change of current(di/dt) = 0.8 As-1
Formula used:
L = μ0n2A/l, where L = self inductance, μ0 = magnetic permeability of vacuum n = number of turns, A = area, l = length
Now, emf 
, where L = self inductance, 
= rate of change of current
Putting the values:
= 
V (Ans)
1