A toroidal solenoid with an air core has an average radius of $15 \,cm$, area if crosssection $12\, cm ^{2}$ and $1200$ turns. Ignoring the field variation across the cross- section of the toroid, the self-inductance of the toroid is:-
Given, radius $=15 \,cm$,
cross $-$ section $=12 \,cm ^{2}, $$N =1200$
The self inductance of toroid is given by:
$1=\frac{\mu_{0} N ^{2} A }{2 \pi r }=\frac{2 \times 10^{-7}(1200)^{2} \times 12 \times 10^{-4}}{0.15}$$=0.000023=2.3 \,mH$
Electromagnetic Induction is a current produced by the voltage production due to a changing magnetic field. This happens in one of the two conditions:-
When we place the conductor in a changing magnetic field.
When the conductor constantly moves in a stationary field.