Answer the following questions, which help you understand the difference between Thomson’s model and Rutherford’s model better.
(a) Is the average angle of deflection of -particles by a thin gold foil predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?
(b) Is the probability of backward scattering (i.e., scattering of `alpha`-particles at angles greater than `90°`) predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?
(c) Keeping other factors fixed, it is found experimentally that for small thickness t, the number of `alpha`-particles scattered at moderate angles is proportional to t. What clue does this linear dependence on t provide?
(d) In which model is it completely wrong to ignore multiple scattering for the calculation of average angle of scattering of `alpha` -particles by a thin foil?

Explanation

(a) About the same. This is because we are talking of average angle of deflection.
(b) Much less, because in Thomson's model, there is no such massive central core called the nucleus as in Rutherford's model.
(c) This suggests that scattering is predominantly due to a single collision, because chance of a single collision increase with the number of target atoms which increases linearly with the thickness of the ofil.
(d) In Thomson model, positive charge is uniformaly distributed in the spherical atom. Therefore, a single collision causes very little deflection. Therefore, average scattering angle can be explained only by considering multiple scattering. Thus it is wrong to ignore multiple scattering in Thomson's model.
On the contrary, in Rutherford's model, most of the scattering comes form a single collision. Therefore, multiple scattering may be ignored as a first approximation.