(a) Compute the charge on the capacitor just before the switch is thrown from po
ID: 1280024 • Letter: #
Question
(a) Compute the charge on the capacitor just before the switch is thrown from position 2 back to position 1. (C)
(b) Compute the voltage drops across the resistor and across the capacitor at the instant described in part (a).
Across the resistor. (V)
Across the capacitor. (V)
(c) Compute the voltage drops across the resistor and across the capacitor just after the switch is thrown from position 2 back to position 1.
Across the resistor. (V)
Across the capacitor. (V)
(d) Compute the charge on the capacitor 60.0 ms after the switch is thrown from position 2 back to position 1. (C)
Explanation / Answer
a)
Maximum Charge
Qo=CVo=(5*10-5)*21=1.05*10-3 C
Time Constant
T=RC =910*5*10-5=0.0455 sec
So in RC circuit Charge as a function of time is given by
Q=Qo[1-e-t/T]
Q=(1.05*10-3)[1-e-0.06/0.0455]
Q=7.7*10-4 C
b)
Voltage across capacitor isr is
Vc=Voe-t/T=21*e-0.06/0.0455
Vc=5.62Volts
Voltage drop across resistor is
VR=21-5.62=15.38 Volts
c)
Voltage drop across capacitor and resistor is
VR=VC=15.38 Volts
d)
Q=Qoe-t/T =(7.7*10-4)e-0.6/0.045
Q=2.03*10-4 C
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