Question

A wire of length $100 \, m$ is tightly wounded on a hollow tube of radius 5mm and length $1 \, m$ . A current of $1 \, A$ is flowing in the wire. Then magnetic field strength inside the tube will be :-

• A. $4T$
• B. $4mT$
• C. $40 \, mT$
• D. $40 \, T$

Answer 1

Answer: (B)

Field due to a solenoid = $\mu _{0} \text{ni}$
Given i = 1 A
$\text{n} = \frac{1 0 0}{2 \pi \times 5 \times 1 0^{- 3}}$
$\therefore \text{B}=\mu _{0}\text{ni}=\frac{4 \pi \times 1 0^{- 7} \times 1 0 0 \times 1}{2 \pi \times 5 \times 1 0^{- 3}}=4\text{mT}$