Question

A coil of wire of a certain radius has $100$ turn and a self-inductance of 15 mH. The self-inductance of a second similar coil of $500$ turns will be :

• A. $75mH$
• B. $375mH$
• C. $15mH$
• D. none of these

Answer 1

The correct option is B $375mH$

Self inductance of a coil of wire = $L=\frac{\mu N^{2}A}{l}$
As the number of turns become $5$ times, the self inductance must become $25$ times the initial value.

Thus new self inductance = $25\times 15mH=375mH$