Concepts

Electric charge, Coulomb's law, induced charge

Overview

A pith ball is charged using a previously charged PVC or glass rod to show attraction of opposite charges and repulsion of like charges.

Details

Equipment

• [1] Pith ball attached to a string
• [1] Plastic bag
  
• [1] Glass rod
• [1] Rabbit fur
• [1] PVC rod
• [1] Lab stand
• [1] 90-degree clamp
• [1] Metal rod
• [1] Bulldog clip

Classroom Assembly

1. Attach the metal rod to the lab stand using the 90-degree clamp.
2. Hang the pith ball using the bulldog clip.

Important Notes

• If you hear a crackling noise during charging, the rod is charging well.
• As with most electrostatic demonstrations, this works best under 50% humidity.

Script

1. Rub the fur on the PVC rod to charge the rod negatively.
2. Bring the PVC rod close to the pith ball. It should attract the neutral pith ball due to induced charge.
   
3. Touch the pith ball with the PVC rod. This makes the pith ball negatively-charged.
4. Hold the PVC rod near the pith ball and show that like charges repel.
5. Rub the plastic bag on the glass rod. The bag rubs some electrons off the rod, making the glass rod positive.
   
6. Hold the glass rod near the pith ball and show that opposite charges attract.
   

Additional Resources