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Calculate the back e.m.f of a 10H, 200 O...

Calculate the back e.m.f of a 10H, 200 `Omega` coil 100 ms after a 100Vdc supply is connected to it.

Text Solution

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The value of current at 100 ms after the switch is closed is
`I = I_0 [ 1 - e^((-1)/(T_0)) ] ` , here , `I_0 =100/200 =0.5` amp
`tau_0 = L/R = 10/200 = 0.05 sec , t = 0.1 sec`
`I = 0.5 (1-e^(0.1//0.05)) = 0.5 (1-e^(-2)) = 0.4325A`
now `E = IR + L (dI)/(dt) ,or 100 = 0.4325 xx200 + L (dI)/(dt)`
back emf = `L (dI)/(dt) = 100 - 0.4325 xx 200 = 13.5V`
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