✓ Board-verified
Physics · 2026 · 3 marks
CBSE 2026 · Region 5 · Set 1 · Q26
(a) (i) Write any two features of nuclear forces. (ii) If both the number of protons and the neutrons are conserved in each nuclear reaction, in what…
(i)
Write any two features of nuclear forces.
(ii)
If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.
(i)
Draw the number of scattered particles versus the scattering angle graph for scattering of alpha particles by a thin foil. Write two important conclusions that can be drawn from this plot.
(ii)
If Bohr's quantization postulate (angular momentum $\displaystyle =\frac{\mathrm{nh}}{2 \pi}$ ) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.
Marking-scheme solution
(i)
Features of nuclear force (any two): charge independent; strongest force; short-range force / saturated force; does not follow the inverse square law.
(ii)
The total mass of the nuclei on the left-hand side need not be the same as that on the right-hand side of a nuclear reaction. Since binding energy contributes to mass, the difference in these binding energies appears as energy released or absorbed in a nuclear reaction.
(i)
Graph between the number of scattered particles and the scattering angle:
Important conclusions: 1. Most of the space in the atom is empty. 2. Most of the mass of the atom and its positive charge were tightly concentrated at its centre.
(ii)
According to the Bohr quantisation postulate, $\displaystyle \mathrm{L}=\mathrm{mvr}=\dfrac{n h}{2 \pi}$. Since the mass of planets is very large compared to the mass of atomic particles, the angular momentum L will be very large.
Therefore the principal quantum number n will be very large. For large quantum number the difference in successive energy levels will be negligible; hence quantisation fails.
More from Nuclei
- Calculate the energy released/absorbed in the following nuclear reaction: _6^12 C+_6^12 C →_10^20 Ne+_2^4 He Given: m(_6^12 C)=12 · 000000 u m(_10^20…2024 · asked 2×
- Two nuclei have their mass numbers in the ratio of 8: 1. The ratio of their nuclear densities is:2023
- Briefly explain how energy is produced in stars, giving two examples of the nuclear reactions involved.2025
- A narrow beam of protons, each having 4.1 MeV energy is approaching a sheet of lead (Z=82). Calculate: (i) the speed of a proton in the beam, and…2022
- Explain the terms mass defect and binding energy. How are they related?2026
- Deuterium undergoes the following fusion reaction: _1^2 H+_1^2 H →_2^3 He+_0^1 n+3.27 MeV How long an electric bulb of 200 W will glow by using the…2024
- (i) Prove that the nuclear density is same for all nuclei. (ii) Draw a plot of potential energy of a pair of nucleons as a function of their…2023
- Calculate the binding energy per nucleon (in MeV ) of a helium nucleus ( _2^4 He ). Given: m(_2^4 He)=4 · 002603 u m_n=1.008665 u; m_H=1.007825 u; 1…2025
CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.