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Old Jul 10th 2010, 02:27 PM   #1
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inductive time constants

A resistance of 100,000 ohms is used to discharge a .47 uF capacitor that is charged to 1500V. a) How many time constants must elapse before the capacitor voltage falls to 10V? b)How much time must elapse?

The only formula that I have for time constant is TC= L/R and I need to account for the fall in V but I'm don't know the formulas and steps to figure this one out.
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Old Jul 10th 2010, 07:42 PM   #2
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There is two more formula that you should remember.

V=V0 * e^(-t/CR) and time constant= CR
if i remember it correctly
V is the potential difference of capacitor at an instant
V0 is the initial potential difference of charged capacitor
t is the time elapsed
CR is the time constant for a circuit with a capacitor and a resistor
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