Two identical bar magnets with a length 10cm and weigth 50 gm-weigth are arranged freely with their like poles facing in a inverted vertical glass tube. The upper magnet hangs in the air above the lower one so that the distance between the nearest pole of the magnet is 3 mm. Pole strength of the poles of each magnet will be

Options

A. `6.64 ampxxm`
B. `2 ampxxm`
C. `10.25 ampxxm`
D. None of these

Answer

A

Explanation

The weight of upper magnet should be balanced by the repulsion between the two magnet
`:. Mu/(4pi).m^(2)/r^(2)=50 gm-wt`
`implies 10^(-7)xxm^(2)/((9xx10^(-6)))=50xx10^(-3)xx9.8`
`implies m=6.64 ampxxm`