A 100 turn rectangular coil ABCD is hung from one arm of a balance. A mass 500 g is added to the other arm to balance the weight of the coil. A current 4.9 A passes through the coil and a constant magnetic field of 0.2 T acting inward is switched on such that only arm CD of length 1 cm lies in the field. How much additional mass ‘m’ must be added to regain the balance?
A 100 turn rectangular coil ABCD is hung from one arm of a balance. A mass 500 g is added to the other arm to balance the weight of the coil. A current 4.9 A passes through the coil and a constant magnetic field of 0.2 T acting inward is switched on such that only arm CD of length 1 cm lies in the field. How much additional mass ‘m’ must be added to regain the balance?

When t = 0, the external magnetic field is off.

Mgl = Wcoil l

0.5 gl = Wcoil l

Wcoil = 0.5 9.8 N

Let m be the mass that is added to restore equilibrium.

The magnetic field is activated when the switch is turned on.

Mgl + mgl = (ILC)l

m = 1 g