Question

A solenoid of 1.5 m length and 4.0 cm diameter possesses 100 turns per meter. A current of 5 amperes is flowing through it. The magnetic induction at axis inside the solenoid is:

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

Answer 1

The correct option is A $2\pi \times {10}^{-3}T$

Magnetic field on the axis for a long solenoid $B={\mu }_{0}ni$ where n is the no of turns per unit length and i is the current in the solenoid
Given:
$n=100$ turns per meter
$i=5$ A
$\therefore B=4\pi \times {10}^{-7}\times 100\times 5=2\pi \times {10}^{-4}T$