Question

The magnetic induction at a distance ‘d’ from the magnetic pole of the unknown strength ‘m’ is B. If an identical pole is now placed at a distance of 2d from the first pole, the force between the two poles is

• A. mB
• B. $\frac{mB}{2}$
• C. $\frac{mB}{4}$
• D. 2mB

Answer 1

The correct option is C $\frac{mB}{4}$

$B=\frac{{\mu }_{0}m}{4\pi d^2}$

$r=2d$

$F=\frac{{\mu }_0{m}_1{m}_2}{4\pi r^2}$

$F=\frac{{\mu }_0\times m\times m}{4\pi (d{)}^2}$

$F=\frac{{\mu }_0{m}^2}{4\pi \times 4d^2}$

$F=\frac{mB}{4}N$