Question

A solenoid has an inductance of $60\text{H}$ and a resistance of $30\Omega$. If it is connected to a $100\text{V}$ battery, how long will it take for the current to reach $63.2\%$ of its steady state value?

• A. $1\text{s}$
• B. $2\text{s}$
• C. $3\text{s}$
• D. $4\text{s}$

Answer 1

The correct option is B $2\text{s}$

The time taken by the current to reach to $63.2\%$ of its steady state value in an $RL$ circuit, is equal to its time constant.

$\therefore t=\tau =\frac{L}{R}=\frac{60}{30}=2\text{s}$

Hence, $\left(B\right)$ is the correct option.