March 2, 2015

Homework Help: Physics- Repost (Answer did not make sense)

Posted by Dan on Saturday, July 28, 2012 at 1:12am.

In the circuit below, at time t = 0, the switch is closed, causing the capacitors to charge. The voltage across the battery is 12 V
The circuit:

A)Calculate the time constant for the RC circuit

B)Calculate the time required for the voltage across the capacitor to reach 6 V

C)What will be the net charge stored in the capacitor after 10 nanoseconds?

What I did:

A) Time constant= [(C1+C2)*(R1R2)]/(R1+R2)
= [(3uF+6uF)*(4k-ohm*2k-ohm)]/(4k-ohm+2k-ohm)
= 12 ms= 0.012 sec?

TC= time constant
B) q= q0[1-e^(-t/TC)]
t= 8.316 ms= 0.008316 sec?

C) I don't know what to do and can't find an equation that I think would work

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