Question

The current in a coil of self-inductance of 4 H changes from 10 A to 2 A in t seconds and the induced e.m.f. is 40 V. The time t is
1. 0.2 s
2. 0.4 s
3. 0.6 s 
4. 0.8 s

Answer 1

Correct Answer - Option 4 : 0.8 s

Concept:

Voltage equation for inductance is:

\({V_L} = L\frac{{di}}{{dt}}\)

Where,

VL is the voltage induced in the coil

L is the inductance of a coil

\(\frac{{di}}{{dt}}\) is the instantaneous value of the rate of change of current

Calculation:

From the given data, we can write:

\(40 = 4\times (\frac{10-2}{t})\)

t = 0.8 sec