Correct AnswerA. increases with the increase of inductance and the decrease of resistance
Quick Explanation
For an RL circuit the time constant is τ=L/R. It increases when inductance increases and when resistance decreases, because larger L resists current change while larger R dissipates energy faster.
Detailed Explanation
Concept & Reasoning
After a DC step, current in a simple series RL circuit approaches its final value exponentially with time constant L/R. Roughly 63.2% of the total current change occurs after one time constant and more than 99% after about five time constants.
How to Solve It in the Exam
L upstairs, R downstairs.
Important Exam PointUse the Thevenin resistance seen by the inductor for more general first-order networks.
Related Revision Path
This question sits in the revision path Signals and Systems → First-Order Circuits → RL Transients .
