Question

A coil of self inductance $2\cdot 5H$ and resistance $20\Omega$ is connected to a battery of emf 120V having internal resistance of $5\Omega$. Find the time constant of the circuit.

Answer 1

Self inductance of coil$=L=2.5H$, Internal resistance of battery$=R=5\Omega$

Time constant $=\tau =\frac{L}{R}$
$\tau =\frac{2.5}{20}$
$=0.125s$