Electrostatic model of alpha particle scattering
Practical Activity for 14-16
This is another model for the scattering of alpha particles; this time using the electrostatic repulsion between the dome of a Van de Graaff generator and a table tennis ball.
Apparatus and Materials
- Table-tennis (ping-pong) ball, coated with Aquadag
- Fine nylon thread
Health & Safety and Technical Notes
If the table-tennis ball suspension is attached to the ceiling, ensure that an adult is available to hold the step-ladder while another adult works at a height.
This electrostatic model gives a fairer illustration of the path of an alpha particle under nuclear repulsion. The magnetic model is the one that Rutherford used in lectures.
- The table tennis ball is coated with Aquadag to make it conducting.
- Attach a long nylon thread to the ball with Sellotape. Suspend the thread so that the suspension is as long as possible - preferably from the ceiling.
- Set up the Van de Graaff generator below the suspension so that the ball can swing freely near the sphere and at the same height.
- With the ball touching the sphere, start the machine so that the two become charged.
- Pull the charged ball to one side with an insulating rod. Let it fall back towards the sphere of the generator and watch its motion.
- Move the suspension (or the Van de Graaff generator) so that the ball passes by the dome and is deflected only a small amount.
- The suspended ball represents the alpha particle which is repelled by the Van de Graaff sphere when both have charges of the same sign.
This experiment was safety-tested in April 2006
- A video showing how to use a Van de Graaff generator: