An inductor coil stores 32 J of magnetic field energy and dissiopates energy as heat at the rate of 320 W when a current of 4 A is passed through it. Find the time constant of the circuit when this coil is joined across on ideal battery.

Explanation

`U=32J` , `P=320W` , `i=4A`
`U=(1)/(2)Li^(2)=32`
`32=(1)/(2)xxLxx(4)^(2) implies L=4H`
`P=i^(2)R`
`320=(4)^(2)R implies R=20Omega`
`tau=(L)/(R)=(4)/(20)=0.2sec`