Consider an RL circuit with R = 1.6k?, L = 240mH and E= 12 V and a switch S. Ima
ID: 1518453 • Letter: C
Question
Consider an RL circuit with R = 1.6k?, L = 240mH and E= 12 V and a switch S. Imagine we put the switchin position a and wait a “long” time. Then we put the switch at position b at t = 0. (i.e., assume that the time is reset to zero at this time.)
a)
What is the initial value for the current, just after the switch is put to position b?
(b)
What is the current after a long time passed since the switch is put to position b?
(c)
How long will it take (from t = 0) for the current to drop to one thirdits initial value?
Explanation / Answer
a) I = E/R = 12/1.6 kohm = 7.5 mA
b) the current =0 because there is no source in the circuit and R dissipate the energy.
C) the time constant tau = L/R = 0.24/1600 = 0.15 ms
I/I0 = exp(-t/tau) = 1/3
t = tau*ln3 = 0.165 ms