The Total solution for NCERT class 6-12
Answer the following questions,which help you understand the difference between Thomson’s model and Rutherford’smodel better.
(a) Is theaverage angle of deflection of α-particles by a thin gold foilpredicted by Thomson’s model much less, about the same, or much greater thanthat predicted by Rutherford’s model?
(b) Is theprobability of backward scattering (i.e., scattering of α-particlesat angles greater than 90°) predicted by Thomson’s model much less, about thesame, or much greater than that predicted by Rutherford’s model?
(c) Keepingother factors fixed, it is found experimentally that for small thickness t,the number of α-particles scattered at moderate angles isproportional to t. What clue does this linear dependence on t provide?
(d) Inwhich model is it completely wrong to ignore multiple scattering for thecalculation of average angle of scattering of α-particles by a thinfoil?
(a) about thesame
The average angle of deflectionof α-particles by a thin gold foil predicted by Thomson’s model isabout the same size as predicted by Rutherford’s model. This is because theaverage angle was taken in both models.
(b) much less
The probability of scatteringof α-particles at angles greater than 90° predicted by Thomson’smodel is much less than that predicted by Rutherford’s model.
(c) Scatteringis mainly due to single collisions. The chances of a single collision increaseslinearly with the number of target atoms. Since the number of target atomsincrease with an increase in thickness, the collision probability dependslinearly on the thickness of the target.
(d) Thomson’smodel
It is wrong to ignore multiplescattering in Thomson’s model for the calculation of average angle ofscattering of α−particles by a thin foil. This is because a singlecollision causes very little deflection in this model. Hence, the observedaverage scattering angle can be explained only by considering multiplescattering.