Nuclei Class 12 Notes Physics Chapter 13

Chapter at a Glance

1. The nucleus of an atom consists of protons + neutrons i.e. nucleons.

10. Average binding energy of nucleus is about 7 to 8 MeV per nucleon. Take it as 7.5 MeV for calculation.

11. The disintegration of heavy elements into comparatively lighter elements by the emission of radiations a, p and y is called radioactivity.

12. a- rays consist of a- particles which are doubly ionised helium ion. P-rays consist of fast moving electrons.
y – rays are electromagnetic waves.

13. Mass number decreases by 4 and atomic number decreases by 2 on the emission of a- particle and increases by 1 on the emission of p particle.

14. The nuclei containing even number of protons and even number of neutrons are most stable.
And the nuclei containing odd number of protons and odd number of neutrons are most unstable.

20. Nuclear forces are saturated (operate only within the nucleus).They are charge independent. If (n, p) is the force between neutron and proton, (n, n) is the force between neutron and neutron, (p, p) is the force between proton and proton, then (n, p) = (n, n) = (p, p)
21. Nuclear forces are both repulsive (when nucleons are near) and attractive (when nucleons are far).
22. The exchange particle for nuclear forces is meson. This means a nucleon exerts a force on another by exchanging a meson.
23. Nuclear fission is the splitting of a heavy nucleus into two or more lighter nuclei

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