Posted by **Stephanie** on Wednesday, March 10, 2010 at 6:30pm.

A 9-Volt battery is used to charge a 280 mF capacitor over a 81 Ohms resistance.

How long will it take for the capacitor to reach 75% of its maximum charge?

What formula is relevant?

- Physical Science -
**sam**, Wednesday, March 10, 2010 at 10:26pm
charging the capacitor formula;

Q=Q max (1-e ^-t/RC)

Q=qmax= 0.75

solve for t

- Physical Science -
**anony mouse**, Thursday, March 11, 2010 at 3:42pm
So the Voltage is irrelevant?

- Physical Science -
**Sandra**, Thursday, March 11, 2010 at 10:25pm
Why wouldn't you use this formula?

Q=Qmax*e^(-t/RC)

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