A series RL circuit with inductance L and resistance R is connected to an emf V. After a time the current reaches a final value of 5.0 A. A second series circuit connected to the same emf V is identical except that the resistor is 4R. The current in the second circuit is
A) 0.80 A.
B) 1.3 A.
C) 1.8 A.
D) 5.0 A.
E) 20 A.

Question

Quizplus · Accepted Answer

The final current in an RL circuit is determined by the applied emf and the resistance in the circuit, given by $I = \frac{V}{R}$. When the resistance is quadrupled (from R to 4R), the final current will be one-fourth of the original, so $5.0 A / 4 = 1.25 A$, which is closest to choice B, 1.3 A.

A Series RL Circuit with Inductance L and Resistance R