Physics Dept. Demonstration Manual

DEM01 - Static Electricity, Basic

Objective: To show basic phenomena of static electricity: production of and interaction between charges.
Apparatus:  
  • Ebonite rod and cat's fur
  • glass rod and silk
  • glass beaker and silk
  • lucite rod and silk
  • pith balls on stand (mass of pith ball = 0.080 ±0.005 g)
  • electroscope
 


Method:

When a glass rod is rubbed with silk, the resulting charge on the rod is positive. However, it is sometimes difficult to achieve much of a net positive on the glass rod. Two much more effective ways are:

  • rub the bottom of a glass beaker with silk. The larger area allows greater charge transfer,
  • rubbing a lucite rod with silk. Electrons are readily transferred from the lucite to the silk.

When an ebonite rod is rubbed with cat's fur the resulting charge on the rod is negative.

The two opposite charges produced are illustrated by using pith balls on stand or an electroscope.

The pith balls on the stand are set on top of the O.H.P. and focussed on the screen. When the positive charge from the rod is transferred to both balls, they will repel each other. Also both of the balls will repel any other positive charge that is brought in. But if the rod with a negative charge is brought in, both balls would be attracted to it, and become neutral if contact occurs.