What is the resistance of a series RL circuit in which L = 73 mH if the current increases to a quarter of its final value in 14 $\mu$s?
A)1.5 k$\varOmega$
B)2.6 k$\varOmega$
C)3.2 k$\varOmega$
D)4.7 k$\varOmega$
E)5.8 k$\varOmega$

Question

Quizplus · Accepted Answer

The time constant of the circuit is given by $\tau = L/R$. The current increases to a quarter of its final value in one time constant, so $\tau = 14 \mu s$. Therefore, $R = L/\tau = 73 mH / 14 \mu s = 1.5 k\Omega$.

What Is the Resistance of a Series RL Circuit in Which