Question

A solenoid 1.5 m long and 0.4 cm in diameter possesses 10 turns per cm length. A current of 5 A falls through it. The magnetic field at the 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}}T $
• D. $ 2\pi \times {{10}^{-3}}T $

Answer 1

Answer: (A)

Magnetic field at the axis inside the solenoid $ B={{\mu }_{0}}ni $ Here, $ n=10\text{ }turns/cm=1000\text{ }turns/m,i=5A $ $ \therefore $ $ B=4\pi \times {{10}^{-7}}\times 1000\times 5 $ $ =2\pi \times {{10}^{-3}}T $