5C30.30-Light the Bulb

Video: Watch this demo

Instructor’s video

Description: This demonstrations shows that a large capacitor can light a bulb for several seconds


  • Digital Power Supply
  • SPDT switch
  • 1F capacitor (rated at 5Vmax)
  • 6.3V Bulb
  • Small c-clamp
  • Wires and alligator clips

Setup Procedure:

  1. Set up the demo according to the configuration in the photos. Wires are color coded to show where each wire connects. Use the black c-clamp to hold the switch in place.
  2. Turn on digital power supply and tune to your desired voltage.  Do not exceed 5V
  3. Test to make sure everything works correctly. The bulb should start off bright and dim as the capacitor charges, and should do the same as the capacitor discharges. 
  4. When the professor is done, make sure the capacitor is discharged.

Demonstration Procedure:

  1. Move the switch to the charge position and wait for the capacitor to charge (the current will be zero when it is fully charged).
  2. Move the switch to the discharge position and note that the capacitor lights the bulb, and the bulb gets dimmer as time goes on.
  3. Repeat if desired.

Concept: Capacitors are electrical components that store charge for use as a power source. Because they only store a finite amount of charge, they can only supply voltage for a limited time. This concept is illustrated in this demo by using a charged capacitor to power a light bulb, but the bulb will eventually die because its power supply is limited.