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ID: 1781531 • Letter: L

Question

LR Time

LR TIME BASE

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Time Dependence of LR Circuit

Three resistors ( R1 = 120 Ohms, R2 = 330 Ohms, and R3 = 240 Ohms) and an ideal inductor (L = 1.6 mH) are connected to a battery (V = 9 V) through a switch as shown in the figure below.


The switch has been open for a long time before it is closed at t = 0. At what time t0, does the current through the inductor ( I3) reach a value that is 63% of its maximum value? t0 = s

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Explanation / Answer

equivalent resistance

Req=120*330/(120+330)+240=328 ohms

Time Constant

T=L/R =1.6*10-3/328

T=4.88*10-6 s

In a RL circuit ,Current through inductor as a function of time is

I=Io(1-e-t/T)

0.63=(1-e-t/4.88*10^-6)

t=4.85*10-6 s