A rectangular, a square , a circular and an elliptical loop, all in the `(x-y)` plane, are moving out of a uniform magnetic field with a constant velocity `vec(v)=vhati` . The magnetic field is directed along the negative `z`-axis direction. The induced emf, during the passage of these loops , out of the field region, will not remain constant for :

Options

A. the rectangular, circular and elliptical loops
B. the circular and the elliptical loops
C. only the elliptical loop
D. any of the four loops

Answer

B

Explanation

Induced emf, `|e|=(dphi)/(dt)=(BdS)/(dt)`
Now, as the square loop and rectangular loop move out of magnetic field, `(BdS)/(dt)` is constant, therefore `|e|` is constant. But in case of circular and elliptical loops, `(dS)/(dt)` changes. Therefore, `|e|` does not remain constant.