Question

The figure shows an $L-R$ circuit, the time constant for the circuit is :

• A. $\frac{L}{2R}$
• B. $\frac{2L}{R}$
• C. $\frac{2R}{L}$
• D. $\frac{R}{2L}$

Answer 1

The correct option is B $\frac{2L}{R}$

By short-circuiting the battery, net resistance across inductor is 2 resistances across it in parallel
i.e.
Hence
${\tau }_{eq}=\frac{L}{R_{eq}}=\frac{L}{R/2}=\frac{2L}{R}$