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A 3000 F supercapacitor charged to 2.7 V stores about

  • A.0.3 Wh
  • B.11 Wh
  • C.3.0 Wh
  • D.30 Wh

Answer: C

Correct answer: 3.0 Wh

The energy in a capacitor is

\[ E = \tfrac{1}{2}CV^2 = 0.5 \times 3000 \times 2.7^2 = 0.5 \times 3000 \times 7.29 \approx 10\,935 \ \mathrm{J} \]\[ \frac{10\,935}{3600} \approx 3.0 \ \mathrm{Wh} \]

Three watt hours from a device the size of a large drink can shows the limitation: a lithium ion cell of the same volume holds perhaps thirty times as much. What the supercapacitor offers instead is the ability to deliver it in a second and to do so a million times.

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