Question

A solenoid $1.5\, m$ long and $0.4\, cm$ in diameter possesses $10$ turns per cm length. A current of $5\, A$ flows through it. The magnetic field at the axis inside the solenoid is

• A. $2\pi \times10 ^{-3}T$
• B. $2\pi \times 10 ^{-5}T$
• C. $4\pi \times 10 ^{-2}T$
• D. $4\pi \times 10 ^{-3}T$

Answer 1

Answer: (A)

Magnetic field at the axis inside the solenoid
$B = \mu_{0}\, ni $
Here, $n = 10$ tums/cm =$ 1000 $ turns/m, $i = 5\, A $
$B = 4\pi \times10^{-7} \times1000 \times5 $
$ = 2\pi \times10 ^{-3} \, T$