Question

A solenoid has an inductance of $60$ henrys and a resistance of $30$ ohms. If it is connected to a $100$ volt battery, how long will it take for the current to reach $\frac{e-1}{e}\approx 63.2\%$ of its final value

• A. 1 second
• B. 2 seconds
• C. e seconds
• D. 2 e seconds

Answer 1

Answer: (B)

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