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5.Magnetism and Matter
medium
Two identical bar magnets with a length $10 \,cm $ and weight $50 \,gm$-weight 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.......$ amp × m$
A
$6.64$
B
$2$
C
$10.25$
D
None of these
Solution
(a)The weight of upper magnet should be balanced by the repulsion between the two magnet
$\therefore \;\frac{\mu }{{4\pi }}.\frac{{{m^2}}}{{{r^2}}} = 50\,gm – wt$
$ \Rightarrow {10^{ – 7}} \times \frac{{{m^2}}}{{(9 \times {{10}^{ – 6}})}} = 50 \times {10^{ – 3}} \times 9.8$
$ \Rightarrow m = 6.64\,amp \times m$
Standard 12
Physics
