Question

37. In Fig, the magn
18. the magnetic needle has magnetic
moment .7*10- Am? and moment of inertia
7.5X10 kg ml. It performs 10 complete
Oscillations in 6.70 s. What is the magnitude of the
magnetic field?
1) 0.2 T
2) 0.05T
3) 0,08 T
4) 0.01T​

Answer 1

As we learnt,

Time period of oscillating Bar magnet -

$T=2\pi\sqrt\frac{I}{MB}$

Wherein,

I = moment of inertia = 7.5*10

M = magnetic moment = 7*10

T = time taken = 6.7

B = magnetic field = ?

$6.7=2\pi\sqrt\frac{7.5*10}{7*10*B}$

$\frac{6.7}{2\pi}=\sqrt\frac{7.5*10}{7*10*B}$

$\frac{{6.7}^{2}}{{2}^{2}*{\pi}^{2}}=\frac{7.5*10}{7*10*B}$

$B=\frac{7.5*10*4}{6.7*6.7*\pi*\pi*7*10}$

$\bold{B=0.01T}$

Here π = 22/7

So, Option (D) is correct.