Question

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

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

Answer 1

Answer: (B)

Field due to a solenoid = ${\mu }_0\text{ni}$
Given i = 1 A
$\text{n}=\frac{100}{2\pi \times 5\times 10^{-3}}$
$\therefore \text{B}={\mu }_0\text{ni}=\frac{4\pi \times 10^{-7}\times 100\times 1}{2\pi \times 5\times 10^{-3}}=4\text{mT}$