The switch in the figure is closed at t = 0 when the current I is zero.When I = 15 mA, what is the potential difference across the inductor?
A)240 V
B)60 V
C)0
D)180 V
E)190 V

Question

The switch in the figure is closed at t = 0 when the current I is zero.When I = 15 mA, what is the potential difference across the inductor? 
A)240 V 
B)60 V 
C)0 
D)180 V 
E)190 V

Quizplus · Accepted Answer

When the switch is closed at t=0, the circuit becomes a simple DC circuit consisting of a resistor R and an inductor L in series. The potential difference across the inductor at any time t can be found using the formula V=L(di/dt) where di/dt is the rate of change of current with time.

Initially, the current is zero, so di/dt is at its maximum, which is equal to E/R (where E is the emf of the battery and R is the resistance). Therefore, at t=0, the potential difference across the inductor is V=L(di/dt)=L(E/R).

As the current increases, the di/dt decreases and the potential difference across the inductor decreases. At steady state, the potential difference across the inductor is zero as the current becomes constant.

At I=15mA, the potential difference across the inductor is V=L(di/dt)=L(d(15mA)/dt)=L(0)=0 (since the current is now constant).

Therefore, the answer is D) 180 V.

The Switch in the Figure Is Closed at T =