An inductor stores magnetic energy U when current i flows through it and dissipates power P. When the coil is connected across an ideal battery, its time constant is:
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Question

An inductor stores magnetic energy U when current i flows through it and dissipates power P. When the coil is connected across an ideal battery, its time constant is:

G1 Physics · Accepted Answer

U=½Li² and P=i²R. Therefore 2U/P=(Li²)/(i²R)=L/R=τ. Hence τ=2U/P, option C.