Physics Lab Activity

Electrostatics - 3

Induction & Polarization


* to observe, describe and explain induction and charging by induction.

Note: You may work with one or two partners for this activity. Discuss the explanations and answers with your partner(s) and write one clear, accurate answer on another sheet of paper. Be sure that all participants put their name on this sheet.


plastic strips

cloth scraps

pith ball with thread

ring stand

ring stand clamp


Styrofoam "peanuts" or a balloon

empty "soda pop" can



Part 1 - Charging by Induction

Follow steps 1 - 4 to charge your electroscope by induction:

  1. Ground the electroscope by touching the top plate with your finger.
  2. Bring a charged strip near the top plate of the electroscope, but not touching it.
  3. Ground the electroscope by touching the top plate with your finger. Be sure that the charged strip is held near (but not touching) the electroscope's top plate while you do this.
  4. After removing your finger from the electroscope, remove the charged rod from near the electroscope's top plate.
  5. How do you know that the electroscope has an electric charge after completing step 4?
  6. Is the charge on the electroscope the same as the charge on the charged strip, or opposite? (Don't just guess - test it!) How do you know?
  7. Write a description of what happens to the electric charges on the electroscope when you follow steps 1 - 4.

Part 2 - Electrical Polarization

  1. Lay an empty "pop" can on its side on your lab table. Bring your charged strip near the can but not touching it. Describe what happens. Why does this happen?
  2. Hang a pith ball and observe what happens when a charged strip is brought near the neutral pith ball. (You did this in the first electrostatics lab.) What happens, and why?
  3. Get some Styrofoam peanuts (or a balloon - be careful blowing it up!). Note that they stick easily to the wall (and you!) after charging. Why?

last update February 14, 2001 by JL Stanbrough