5C30.20 Short a Capacitor


Charging and discharging of a capacitor, energy stored in a capacitor


A large capacitor is charged by a 6 V battery or a 15 V DC power supply. When a copper rod is shorted across the terminals of the capacitor, a large spark is produced. The spark is obviously more dramatic at 15 V than at 6 V.



  • [1] Capacitor bank
  • [1] 6 V battery or 15 V DC power supply
  • [2] Banana cable
  • [4] Insulated alligator clip
  • [1] Copper rod
  • [1] Abrasive cloth

Safety Equipment

  • [1] Safety glasses
  • [2] Safety glove

Classroom Assembly

  1. Rub the abrasive cloth on the copper rod to remove surface oxides.

Important Notes

  • Make sure the capacitor is completely discharged before handling.
  • The most dramatic sparks occur when you short the capacitors on sharp edges of the electrodes. For best results, keep the copper rod in contact with one electrode and slowly tilt the rod towards the other electrode.
  • Do not overcharge the capacitors, which are rated to 15 V.


  1. Put on your safety goggles and gloves.
  2. Charge the capacitor by connecting the terminals to the battery or power supply. The battery should be connected for at least 10 seconds.
  3. Disconnect the battery or power supply.
  4. Short the capacitor using the copper rod.


Additional Resources


  • PIRA 5C30.20


  • Don't attempt this at home!

Last revised

  • 2020


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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.