Question

A long solenoid of radius $1 \,mm$ has $100$ turns per $mm$. If $1 \,A$ current flows in the solenoid, the magnetic field strength at the centre of the solenoid is :

• A. $6.28 \times 10^{-4} T$
• B. $6.28 \times 10^{-2} T$
• C. $12.56 \times 10^{-2} T$
• D. $12.56 \times 10^{-4} T$

Answer 1

Answer: (C)

$B =\mu_{0} ni =\mu_{0} \frac{ N }{\ell} i$
$\therefore B =4 \pi \times 10^{-7} \times \frac{100}{10^{-3}} \times 1$
$=12.56 \times 10^{-2} T$