Balloon and Vermiculite
Balloon and Vermiculite

 

Code Number: 5B30.10

Demo Title: Charge Density - Balloon

Condition: Excellent

Principle: Surface Charge Density

Area of Study: Electricity and Magnetism

Equipment: 

Balloon, charging cloth, Vermiculite, puffed rice, electrometer and sensing cage.

Procedure:

Blow up the balloon to a good diameter but do not tie it off.  Charge the balloon by rubbing it with the wool cloth.  Bring the balloon near the Vermiculite or the puffed rice and observe how it jumps to and from the  balloon.  Now deflate the balloon to a very small diameter and again bring it close to the Vermiculite or puffed rice.  Observe how the effect is larger with the smaller diameter balloon.  The amount of charge on the balloon is the same, but the charge density is greatest on the smaller diameter balloon.  The Vermiculite seems to work very well with this demonstration.

References:

  • George M. Hopkins, "Frictional Electricity", Experimental Science, p. 362.
  • Borislaw Bilash II, David Maiullo, "Charge Density on a Balloon - Size Matters!", A Demo a Day: A Year of Physics Demonstrations, p. 252.