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Find the value of t/(time constant) for which the current in an L/R circuit builds upto (a)99% and (b)99.9% of steady state value(1)4.6,6.9(2) 6.9,4.6(3) 2.3, 6.9(4)6.9,2.3 |
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Answer» We know the Current formula in L/R circut I(t) = Io [1 - e-t/τ ] , where Io = ε/R is the maximum current and the time constant τ = L/R if current reaches 99 % of steady state, then [1 - e-t/τ ] = 0.99 or e-t/τ = 0.01 = 10-2 . Hence t/τ = 2 × ln10 = 4.6 if current reaches 99.9 % of steady state, then [1 - e-t/τ ] = 0.999 or e-t/τ = 0.001 = 10-3 . Hence t/τ = 3 × ln10 = 6.9 |
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