Energy Stored by a Capacitor

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Energy of a Capacitor - QV Graphs

The work done on a charge (Q) in moving through a potential difference of ΔV is equal to QΔV. This helps to find the energy stored by a capacitor.

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Transporting charge

  • Imagine a parallel plate capacitor that has a potential difference of V. The definition of capacitance says that Q = CV.
  • By transporting a tiny amount of charge, ΔQ, from the negative plate to the positive plate, the potential difference is approximately constant.
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Area under graph

  • The increase in energy stored is equal to the energy gained by the charge, i.e. VΔQ. This is equal to the area shaded on the graph.
  • This means that the total energy stored will equal the area of the triangle: ½QV.

Capacitor Equations

Capacitors are easy to handle if you know what equation to use.

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  • Definition of capacitance:
    • C=QVC=\frac{Q}{V}
  • Capacitance of a parallel plate:
    • C=Aϵ0ϵr/dC=A{{\epsilon}_0}{{\epsilon}_r}/d
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  • The energy stored in a capacitor is:
    • E=12QVE=\frac{1}{2}QV
  • By using the definition of capacitance, you can rearrange to get:
    • E=12CV2E=\frac{1}{2}CV^2
    • E=12Q2CE=\frac{1}{2}\frac{Q^2}{C}

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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