a 460 ohm resistor, an uncharged 1.4 microfarad capacitor, and a battery with a

Question

a 460 ohm resistor, an uncharged 1.4 microfarad capacitor, and a battery with a 6.11 V potential difference are connected in series.

R=460 ohms

C=1.4 microfarads

change in V=6.11 V

A. what is the initial current, in mA, immediately after they are connected. (answer=13.28)

B. What is the RC time constant in seconds? (answer=6.44*10^-4)

C. What is the current, one time constant after they are connected, in milliamps? (answer=4.88)

D. What is the voltage on the capacitor after one time constant in V? (need help answering this)

Explanation / Answer

D)
Charge on the Capacitor after 1 time Constant is given by,

Q = Qf * (1 - e^-(t/RC))
Q = Qf * (1 - e^-1)
Now We know Q = C*V

So,
C*V = C*Vf * (1 - e^-1)
V = Vf * (1 - e^-1)
V = 6.11 *(1 - e^-1)
V = 3.86 V
Voltage on the capacitor after one time constant, V = 3.86 V

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