Equipment

• Separable cylinder conductor/semi-sphere conductor
• Tripod Stand
• Conductor holder
• Gold leaf electroscope
• Proof ball
• Polyethylene rod
• Nylon cloth

Demo

This demo shows that electric charge will occupy the outer surface of a conductor. The polyethylene rod may be charged by conduction by rubbing it with the nylon cloth. The rod may then be used to charge the conductor. The proof ball is then placed against the outside of the conductor, then moved to the electroscope. The leaves of the electroscope will deflect. The charging process is repeated, but this time touch the proof ball to the inside of the conductor; the leaves of the electroscope will not deflect.

Explanation

The proof ball gathers charge when in contact with the outside of the charged conductor, since charge resides on the outer surface of a conductor. This is because conductors are composed of free electrons. When placed in external electric field, the electrons migrate to one side of the conductor and an electric field is created inside the conductor itself due to separation of positive and negative charges. This may be seen in Figure. This electric field is equal in magnitude to the external field, effectively neutralizing the external field (this is why the field inside a conductor is zero). When the proof ball touches the inside surface of the conductor, it gains no charge since the inside of the conductor is neutral.

Written by Madison Harris