Posted by **J** on Monday, February 4, 2008 at 5:56pm.

A 450 uF capacitor is charged to 295 V. Then a wire is connected between the plates. How many joules of thermal energy are produced as the capacitor discharges if all of the energy that was stored goes into heating the wire?

I am totally confused I don't even know where to start. Help please!

- Physics -
**Damon**, Monday, February 4, 2008 at 6:16pm
Gee, I guess I better figure out how much energy is stored in a capacitor at voltage Vf and capacitance C

C = q/V

q = V C

dq/dt = i = C dV/dt

power = i V

power = C V dV/dt

so

power dt = C V dV

integral power dt = Energy = C integral V dV from V = 0 to V = Vf

but integral of x dx = (1/2)x^2 + constant

so

Energy at Vf = (1/2)C Vf^2

ok, now we can use that

Energy = (1/2)(450*10^-6)(295)^2

or

19.6 Joules

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