Statement I : For the scattering of $\alpha$-particles at large angles, only the nucleus of the atom

Question

Statement I : For the scattering of $\alpha$-particles at large angles, only the nucleus of the atom is responsible.\ Statement II : Nucleus is very heavy in comparison to electrons.

Professor PC Thomas Classes · Answer

(a) : We know that an electron is a very light particle as compared to an $\alpha$-particle. Hence electron cannot scatter the $\alpha$-particle at large angles, according to law of conservation of momentum. On the other hand, mass of nucleus is comparable with the mass of $\alpha$-particle, hence only the nucleus of atom is responsible for scattering of $\alpha$-particles. But that is due to Coulombic repulsion offered by positive nucleus to positive $\alpha$-particles.