Question

How does the alpha-particle scattering experiment imply that the nucleus has a positive charge?

I have a textbook which says that from the results of the 1908 alpha particle scattering experiment by Rutherford, Geiger and Marsden shows that the nucleus has a positive charge but I don't see why this has to be?

Answer 1

The trajectories, particularly the `alpha` particles that returned straight out, could not do this if they were attracted to the nucleus.

Explanation:

The exchange of momentum requires the forces acting on the `alpha` particle to be repulsive. Attractive forces would create a different distribution of trajectories.

I agree, it is not obvious and the text books never give a reason, but this is the best I’ve come up with in many years of teaching it.