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An electromagnet has stroed 648 J of mag...

An electromagnet has stroed 648 J of magnetic energy, when a current of 9 A exists in its coils. What average e.m.f. is induced if the current is reduced to zero in 0.45

Text Solution

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Her, `E = 648 J, I = 9 A, e =?`
`dI = 9 - 0 = 9 A, dt = 0.45 s`
From `E = (1)/(2) LI^(2)`
`648 = (1)/(2) xx L (9)^(2)`,
`L = (648 xx 2)/(9 xx 9) = 16 H`
As `e = (L dI)/(dt) :. e = (16(9))/(0.45) = 320 V`
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