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)

$2\pi \times10 ^{-3}T$

Answer 2

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