The energy (in Joules) stored in a capaci- tor with capacitance C (in Farads), h

Question

The energy (in Joules) stored in a capaci- tor with capacitance C (in Farads), having a potential difference V (in volts), is given by W = 1CV2. One application is in the 2 electronic photoflash or strobe light. In such a unit, a capacitor of 11.9 µF is charged to 260 V.

-Find the energy stored. Answer in units of J.

-Find the power required to charge the capacitor to this energy level in 32 s.
Answer in units of W.

-When this capacitor is discharged through the strobe lamp, it transfers all its energy in 0.00015 s.
Find the power delivered to the lamp. Answer in units of kW.

Explanation / Answer

The equation for energy stored in a capacitor is U=(1/2)CV2, therefore the energy stored in this capacitor is (1/2)(11.9*10-6)(2602) = .402J

Power is defined as Energy per unit time, or U/t. Taking 32 seconds to charge takes .402J/32s = .0126W

Again as energy per unit time, to discharge the .402J over only .00015s is .402J/.00015s = 2680W = 2.68kW

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