Question

A solenoid of 2.5 metre length and 2.0 cm diameter possesses 10 turns per cm. A current of 0.5 ampere is flowing through it. The magnetic induction at axis inside the solenoid is :

• A. $2\pi\times10^{-4}\,tesla$
• B. $2\pi\times10^{-5}\,tesla$
• C. $2\pi\times10^{-6}\,tesla$
• D. $2\pi\times10^{-7}\,tesla$

Answer 1

Answer: (A)

$B = \mu_0 \,nl$, where n = number of turns per unit length,
I = current, $\mu_0 = 4 \, \pi \times 10^{-7} \, TA^{-1}$m .
Here $ n =10 \, cm^{-1} = 1000m^{-1}, I $ = 0.5 A,
Hence $B = 4 \, \pi \times 10^{-7} \times 1000 \times 0.5 $
= $2 \, \pi \times 10^{-4}$ T.