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

Answer 1

when distance is r,
F=4.8N=initial force
when the distance is doubled the force reduces to 1 by fourth of initial force
therefore when distance is 2r,
F=1/4×4.8N=1.2N.
where F is final force.

Answer 2

Answer:

for two identical short bar magnet the force is inversely proportional to the r^4