Q.

A massless square loop of wire of resistance 10Ω supporting a mass of 1 g hangs vertically with one of its sides in a uniform magnetic field of 103 G, directed outwards in the shaded region. A dc voltage V is applied to the loop. For what value of V, the magnetic force will exactly balance the weight of the supporting mass of 1 g          [2023]

(If sides of the loop = 10 cm, g=10 ms-2)

1 110 V  
2 100 V  
3 1 V  
4 10 V  

Ans.

(4)

Fm=mg

  ILB=mg

  (vR)LB=mg

  v=mgRLB=(1×10-3 kg)(10 m/s2)(10Ω)(0.1 m)(103×10-4 T)=10 V