The current `i` in a coil varies with time as shown in the figure. The variation of induced emf with time would be

Options

A.
B.
C.
D.

Answer

A

Explanation

Induced emf is `e = - L (di)/(dt)`
In Fig.
During 0 to `(T)/(4), (di)/(dt) =` a constant , as i- t graph is a straight line with positive constant slop. Therefore, e is negative and constant.
For time, `(T)/(4) le t le (T)/(2) , (di)/(dt) = 0`, gas i-t graph is a
straight line parallel to t-axis. Therefore, e = 0
For time, `(T)/(2) le t le (3T)/(4). (di)/(dt)` a negative constant,
as i-t graph is a strainght line with negative slope. Therefore, e is + ve and constant.
For time `(3T)/(4) le t leT, (di)/(dt) = 0` therefore, e = 0.
Hence, the variation of induced emf (e) with time (t) will be as shown in option (a) of Fig