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Question

A coil has an inductance of $$50mH$$ and a resistance of $$0.3\Omega$$. 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 A $$40J$$
$${i}_{0}=\cfrac{E}{R}=\cfrac{12}{0.3}=40A$$
$$U=\cfrac { 1 }{ 2 } L{ { i }_{ 0 } }^{ 2 }$$
$$=\cfrac { 1 }{ 2 } \times 50\times { 10 }^{ -3 }{ \left( 40 \right)  }^{ 2 }=40J$$

Physics
NCERT
Standard XII

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