A magnetic needle has magnetic monent 6.7 x 10-2 Am2 and moment of inertia I = 7.5 x 10-6 kgm2 . It performs 10 complete oscillation in 10s. Find the magnetitude of the magnetic field.

The time period of oscillation will be given as

now, we know that the magnetic field in terms of moment of inertia, time period and magnetic moment is given as

here

I = 7.5 x 10-6 kgm2

m = 6.7 x 10-2 Am2

and T = 0.67 s

so,we have

or the magnetic field strength will be

B = 0.01 T

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