Question

When the current in a coil changes from 2 amp. to 4 amp. in 0.05 sec., an e.m.f. of 8 volt induced in the coil. The coefficient of self inductance of the coil is

• A. 0.1 henry
• B. 0.2 henry
• C. 0.4 henry
• D. 0.8 henry

Answer 1

The correct option is B 0.2 henry

Induced e.m.f. $ϵ=\frac{d\varphi }{dt}$
$=\frac{dBA}{dt}=A_0\frac{dB}{dt}$

$=A_0\left(\frac{4B_0-B_0}{t}\right)=3A_0{B}_0/t$