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A camera flash capacitor of 200 microfarads is charged to a potential difference of 100 V. Using U_E = (1/2) C V^2, how much energy does the capacitor store?
A1.0 J
B2.0 J
C0.5 J
D10 J
Answer & Solution
Correct answer: A. 1.0 J
1. U_E = (1/2) C V^2 = (1/2)(200 x 10^-6 F)(100 V)^2.
2. (100 V)^2 = 1.0 x 10^4 V^2, so U_E = (1/2)(200 x 10^-6 F)(1.0 x 10^4 V^2) = 1.0 J.
3. This is enough energy to lift a 1 kg ball about 1 m off the ground, released in a flash lasting about a thousandth of a second.
_Source: OpenStax Physics (CC BY 4.0), Ch 18 "Static Electricity", section 18.5 Capacitors and Dielectrics_
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