Homework Help: Physics

Posted by Sandhya on Saturday, May 23, 2009 at 6:04am.

A 12 V battery is connected to 5 mega ohm resistor and a 6 micro farad capacitor and an open switch. After how many seconds will the voltage across the resistor reach 9 V?
Suppose the battery is replaced by 12 V ac with a frequency of 60 Hz.Calculate the Irms in the circuit

Physics - bobpursley, Saturday, May 23, 2009 at 7:35am
If the resistor is 9v, the capacitor is 3 volts.

Vc=q/C=12/(5E6*6E-6)*e^-t/rc

3*30/12=e^-t/30
take the ln of each side, solve for t.
check my typing, my eyes are blurry this am.

Now for the ac part, Z=5E6+1/(2PI60)*6E-6 figure that, it is nearly all resistive.
Then I=12/Z
I can check your work on this.

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