Charged rods brought near the electroscope: Observational Experiment


How does the electroscope work?

Prior Knowledge

  • Model of charge
  • Conductors and dielectrics

Description of the Experiment

First a positively charged rod (clear plastic rubbed with fur) is brought close to the plate of the electroscope but does not touch the plate. Then the same is repeated with a negatively charged pipe (foam insulation pipe rubbed with felt). The plate is connected directly to the indicator mechanism in the middle and is insulated from the circular metal housing.

Observe what happens and come up with an explanation for what you see using your models of charge and conductors.

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.


  1. Observe the first part of the experiment (with a clear rod), record your observation. Make sure that you record what happens when the rod approaches and when it moves away from the plate.
  2. Explain the observation using your knowledge of electric interactions and the internal structure of conductors. Draw a picture to clarify your reasoning, decide how you will represent electric charges inside the conductor.
  3. Observe the second part of the experiment (with a foam pipe) and record your observations.
  4. Explain, use a picture to clarify.
  5. Explain why in both experiments the leaf of the electroscope goes back to the original position.
  6. What do you think will happen if each rod has a larger charge? Smaller charge?