Question

A solenoid (air core) ahs 400 turns, is 20 cm long and has a cross section of $4c{m}^2$. Then the coefficient of self induction is approximately

• A. $4\times {10}^{-5}H$
• B. $4\times {10}^{1}H$
• C. $4\times {10}^{-4}H$
• D. $4H$

Answer 1

The correct option is C $4\times {10}^{-4}H$

$n=400turns,l=20cm,A=4c{m}^2$
$L=?$
$L=\frac{1\cdot 25\times {10}^{-6}H{m}^{-1}\times 400\times 400\times 4\times 100}{100\times 100\times 20}$
$=4\times {10}^{-4}H$