This equation just expresses conservation of energy withhνbeing the photon energy andW the
binding energy of electrons in the solid. Data from the Photoelectriceffect strongly supported the
hypothesis that light is composed of particles (photons).
2.3 The Rutherford Atom*
The classical theory of atoms held that electrons were bound to a large positive charge about the
size of the atom. Rutherford scattered charged (α) particles from atoms to see what the positive
charge distribution was. With a approximately uniform charge distribution, his 5.5 MeVαparticles
should never have backscattered because they had enough energy to overcome the coulomb force
from a charge distribution, essentially plowing right through the middle.
He found that theαparticles often scattered at angles larger than 90 degrees. His data can be
explained if thepositive nucleusof an atom is very small. For a very small nucleus, the Coulomb
force continues to increase as theαapproaches the nucleus, and backscattering is possible.