Spark image

Distance of closest approach

This animation shows the distance of closest approach between an alpha particle and a gold nucleus. The greater the energy of the alpha the closer to the nucleus it will reach before its velocity is reduced to zero and it is repelled.

The distance of closest approach (dc) for an alpha particle of energy Ea is given by the formula :

Ea = qVE =(1/4peo)qQ/dc so therefore dc = (1/4peo)qQ/Ea

Press Start to begin the animation and then Reset followed by Start to fire another alpha particle of different energy at the nucleus.

© Keith Gibbs/John Bourne 2016