5K40.85 Weight-Powered Light


Generators, motors, transformations of energy


A DC motor/generator is connected to a light bulb. When a mass spins the generator, the light bulb emits light.



  • [1] Mounted DC motor
  • [1] Lab stand
  • [2] 90-degree clamp
  • [1] 200 g mass

Classroom Assembly

  1. Secure the motor to the lab stand with the clamps.
  2. Wind up the string attached to the motor.

Important Notes

  • The light bulb isn't very bright. The room should be as dark as possible.


  1. Hook the mass onto the string.
  2. Turn off as many room lights as possible.
  3. Let the mass drop.


Additional Resources


  • PIRA 5K40.85


  • Don't attempt this at home!

Last revised

  • 2017


  • Could try a larger mass if the light is not bright enough.

Related AV

Related demos

  • Hand-cranked generators


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.