Electromagnetic Induction - Result Question 9

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

[2011]

(a)

(b)

(c)

(d)

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Answer:

Correct Answer: 9. (a)

Solution:

  1. (a) $e=-L \frac{di}{dt}$

During 0 to $\frac{T}{4}, \frac{di}{dt}=$ const.

$\therefore e=-ve$

During $\frac{T}{4}$ to $\frac{T}{2}, \frac{di}{dt}=0$

$\therefore e=0$

During $\frac{T}{2}$ to $\frac{3 T}{4}, \frac{di}{dt}=$ const.

$\therefore e=+ve$

Thus graph given in option (a) represents the variation of induced emf with time.

Inductance does not play any role till there is a constant current flowing in the circuit. It opposes any change in the current in the circuit.