A rectangular conducting loop PQRS is kept in xy plane with its adjacent sides parallel to x and y axes. A mag- netic field `vec(B)` is switched on in the region which varies in posi- tion and time as `vec(B) = [B_(0) sin (ky – omega t)]hatk` . It was found that the emf induced in the loop is always zero. Express the length (L) of the loop in terms of constant k and `omega`.

Answer

`L = n (2pi)/(k); n = 1,2,3,..`