Question

Four very long wires are arranged as shown in the figure, so that their cross-section forms a square, with connections at the ends so that current $I$ flow through all four wires. The length of each side, of the formed square cross-section, is $b$ . The magnetic field at the central point $P$ (centre of the square) is

• A. $\frac{\mu _{0} I}{\pi b}$
• B. $\frac{2 \mu _{0} I}{\pi b}$
• C. $0$
• D. $\frac{\mu _{0} I}{\sqrt{2} \, \pi b}$

Answer 1

Answer: (B)

net field $=2\sqrt{2} \, B$
where $B \, = \, \frac{\left(\mu \right)_{0} I}{2 \pi \left(\right. \frac{b \, \sqrt{2}}{2} \left.\right)}$
$\therefore \, $ net field $=\frac{2 \mu _{0} I}{\pi b}$