Question

Force between two identical bar magnets whose centres are $r$ metre apart is $4.8N$, when their axes are in the same line. If separation is increased to $2r$, the force between them is reduced to.

• A. $0.3N$
• B. $0.6N$
• C. $2.4N$
• D. $1.2N$

Answer 1

The correct option is D $1.2N$

Force acting between the bar magnets $F\propto \frac{1}{r^2}$

where $r$ is the separation between the two bar magnets.

Thus if the separation between them is increased by $2$ times, the force between them gets reduced by $4$ times.

So, the new force becomes $F^{\prime }=\frac{F}{4}=\frac{4.8}{4}=1.2N$