Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

Electrostatic model of alpha particle scattering


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

Van de Graaff generator

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. (See Magnetic model of alpha particle scattering). 

A video demonstration of the Van de Graaff generator is available at the National STEM Centre eLibrary.



a The table tennis ball is coated with Aquadag to make it conducting. 

b 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. 
c 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. 
d With the ball touching the sphere, start the machine so that the two become charged. 
e 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. 
f Move the suspension (or the Van de Graaff generator) so that the ball passes by the dome and is deflected only a small amount. 

Aparatus set-up

Teaching notes

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


Related guidance

The great scattering experiments

Evidence for the hollow atom

Developing a model: the nuclear atom

Alpha particles as tools


Related experiments

Alpha particle scattering

Display of cloud chamber photographs

Magnetic model of alpha particle scattering

Gavitational model of alpha particle scattering