The switch in the figure ( Figure 1 ) has been in position a for a long time. It

Question

The switch in the figure (Figure 1) has been in position a for a long time. It is changed to position b at t=0s.

1) What is the charge

The switch in the figure (Figure 1) has been in position a for a long time. It is changed to position b at t=0s. What is the charge Q on the capacitor immediately after the switch is closed? What the current I through the resistor immediately after the switch is closed? What is the charge Q on the capacitor at t=50?s? What is the current I through the resistor at t=50?s? What is the charge Q on the capacitor at t=200?s? What is the current I through the resistor at t=200?s?

Explanation / Answer

1) just after closed still fully charged

Q = Cv = 4*9 = 36 uC

2) I = V/R = 9/25 = 0.36 A

3) q = q0 e^(-t/tau) = 36*e^(-50.0E-6/(4.0E-6*25))= 21.84 uC

4) I = I0 e^(-t/tau) = 0.36*e^(-50.0E-6/(4.0E-6*25))= 0.218 A

5)
q = q0 e^(-t/tau) = 36*e^(-200.0E-6/(4.0E-6*25))= 4.872 uC

6) I =
I0 e^(-t/tau) = 0.36*e^(-200.0E-6/(4.0E-6*25))= 0.0487 A

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