A) 6.64 amp ´ m
B) 2 amp ´ m
C) 10.25 amp ´ m
D) None of these
Correct Answer: A
Solution :
The weight of upper magnet should be balanced by the repulsion between the two magnet \[\therefore \ \frac{\mu }{4\pi }.\frac{{{m}^{2}}}{{{r}^{2}}}=50gm-wt\] \[\Rightarrow {{10}^{-7}}\times \frac{{{m}^{2}}}{(9\times {{10}^{-6}})}=50\times {{10}^{-3}}\times 9.8\] \[\Rightarrow m=6.64amp\times m\]
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