Question

A 10 V battery connected to 5 $\Omega$ resistance coil having inductance 10 H through a switch drives a constant current in the circuit. The switch is suddenly opened and the time taken to open it is 2 ms. The average emf induced across the coil is

• A. 4 × 104 V
• B. 2 × 104 V
• C. 2 × 102 V
• D. 1 × 104 V

Answer 1

Answer: (D)

1 × 104 V

Answer 2

Here, current $\mathrm { I } = \frac { \mathrm { V } } { \mathrm { R } } = \frac { 10 } { 5 } = 2 \mathrm {~A}$

Final current, when the switch is opened is zero

As $\theta = - \mathrm { L } \frac { \mathrm { dI } } { \mathrm { dt } }$

$= - 10 \left( - 1 \times 10 ^ { 3 } \right) = 10 ^ { 4 } \mathrm {~V}$