How many seconds after the switch in an RL circuit is closed will it take the current i to reach 40% of its steady state value? Express answer in terms of R and L and round coefficient to the nearest hundredth.
A) 0.92 L/R seconds
B) 0.51 L/R seconds
C) 1.12 L/R seconds
D) 0.71 L/R seconds

Question

Quizplus · Accepted Answer

The time it takes for the current to reach 40% of its steady state value in an RL circuit is given by the equation:
t = 0.69 * L / R
where t is in seconds, L is the inductance in henries, and R is the resistance in ohms.
Substituting the given value of 40% or 0.4 for I/Io, we have:
0.4 = 1 - e^(-t * R / L)
Solving for t, we get:
t = 0.51 * L / R
Rounding off to the nearest hundredth, we get the answer as choice B, 0.51 L/R seconds.

How Many Seconds After the Switch in an RL Circuit