CBSE 2023 · Region 4 · Set 2 · Q28 · 3 marks
(a)Differentiate between 'impact parameter' and 'distance of closest approach' in alpha particle scattering experiment. Identify, situations when impact parameter is (i) minimum, and (ii) very large.(b)An electron cannot revolve around the nucleus in a hydrogen atom at an arbitrary distance. Explain.
(a)
Differentiate between 'impact parameter' and 'distance of closest approach' in alpha particle scattering experiment. Identify, situations when impact parameter is (i) minimum, and (ii) very large.
(b)
An electron cannot revolve around the nucleus in a hydrogen atom at an arbitrary distance. Explain.
Marking-scheme solution
(a) Difference between Impact Parameter and distance of closest approach $\displaystyle 1$
(b) Explanation
$\displaystyle 1$ (a)
Impact parameter is the perpendicular distance of the initial velocity vector of the \(\displaystyle \alpha\) - particle from the centre of the nucleus.
Distance of closest approach: It is the minimum distance between the projected \(\displaystyle \alpha\) - particle and the nucleus of target atom at which the kinetic energy of the \(\displaystyle \alpha\) - particle becomes equal to potential energy of \(\displaystyle \alpha\) - particle in the field of nucleus.
Minimum: When \(\displaystyle \alpha\) - particle rebounds back \(\displaystyle (\theta=\pi)\)
Very large: when \(\displaystyle \alpha\) - particle goes nearly undeviated and has a small deflection \(\displaystyle \left(\theta=0^{\circ}\right)\)
(b)
According to Bohr's second postulate electron revolves only in those orbit for which angular momentum is \(\displaystyle \frac{\mathrm{nh}}{2 \pi}\). The observed spectral lines of hydrogen atom confirms this.
AtomsAlpha-particle Scattering and Rutherford’s Nuclear Model of AtomUnderstandshort_answermedium
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CBSE Class 12 Physics past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.