Question

A coil has an inductance of 2.5 H and a resistance of 0.5 r. If the coil is suddenly connected across a 6.0 volt battery, then the time required for the current to rise 0.63 of its final value is

• A. 3.5 sec
• B. 4.0 sec
• C. 4.5 sec
• D. 5.0 sec

Answer 1

Answer: (D)

5.0 sec

Answer 2

$t = \tau = \frac { L } { R } = \frac { 2.5 } { 0.5 } = 5 \mathrm { sec }$