Posted by Katie on Sunday, May 22, 2011 at 8:07pm.
How long will it take a charged 80ìF capacitor to lose 20 percent of its initial energy when it is allowed to discharge through a 45 ohm resistor?

Physics  Katie, Sunday, May 22, 2011 at 8:08pm
i mean 80 microfarads

Physics  drwls, Sunday, May 22, 2011 at 8:39pm
The time constant for charge decay is
RC = 3.6*10^3 s, if your ì symbol means "micro"
For 80% of the initial energy, the charge must decrease to sqrt(0.8) = 89.4% of the initial value.
exp(t/RC) = 0.894
t/RC = .1121
t = 4*10^4 seconds
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