A coil has an inductance of 50mH and a resistance of 0.3Ω. If 12V emf is applied across the coil, the energy stored in the magnetic field after the current has built up to its steady state value is
A
40J
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B
40mJ
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C
20J
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D
20mJ
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Solution
The correct option is A40J i0=ER=120.3=40A U=12Li02 =12×50×10−3(40)2=40J