Draw a schematic arrangement of the Geiger Marsden experiment. How did the scattering of `alpha` particles by a thin foil of gold provide an important way to determine an upper limit on the size of nucleus? Explain briefly.

Explanation

Both the nucleus and an alpha particle are
positively charged. When an alpha particle
approcaches a nucleus, it is repelled, the velocity
and hence KE of `alpha` particle goes on decreasing.
in turn, potential energy of the system goes on
increasing. At a cartain distance, the entire KE
of `alpha` particlel is converted into P.E. the alpha
particle can no longer go closer to the nucleus.
This distance of closet approach of `alpha` particle
gives us the approxiate size of the nucleus.