Question

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 α-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 α-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 α-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 α-particles by a thin foil?

Answer 1

(a)

The average angle of deflection of αparticle by thin gold foil predicted by Thomson’s model is about the same size predicted by Rutherford’s model because the average angle taken in both the model.

(b)

In Rutherford’s models alpha ( α ) particles is bombarded on solid gold foil. In this experiment some alpha particles are not deflected, some bounce back and some scattered at an angle from its own path.

Thus, probability of scattering of α particle at angle greater than 90° predicted by Thomson’s model is much less than that predicted by Rutherford’s models.

(c)

The scattering is depends on the single collision. The single collision is more with large number of target atoms.

Thus, number of target atoms increase with increase in thickness and collision probably depends on the thickness of the target.

(d)

Thomson’s model is completely wrong to ignore multiple scattering for the calculation of average angle of scattering of αparticle because single collision cause very little deflection in this model. The multiple scattering is used to calculate the average scattering angle.