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14. A magnetic needle has magnetic moment
5.8 x 10-2 A m and moment of inertia of
7.8 x10^{-6) Kgm^2 , it performs 12 complete oscillations
in 6.0 s. What is the magnitude of magnetic field?
(a) 0.011 T
(c) 0.031 T
(b) 0.021 T
(d) 0.041 T