Nuclei Class 12 Notes Physics Chapter 13 - CBSE

Chapter : 13

What are Nuclei ?

Topic/Term Formula Symbol Representation Important Points
Radius Nucleus R = R0A1/3
  • Most of the space in atom is empty.

  • N(θ) ∝(1/sin4(θ/2))

    • where N(θ) = number of α particles
    θ = scattered angle
 R0 = an empirical constant = 1.1 × 10–15 m
A = mass number of atom
  • Nuclear radius is measured in fermi.

1 fermi = 10–15 m
Nuclear Density p= (M/V) M = mass of nucleus
V = volume of nucleus
  • Density of nuclear matter is of the order of 1017 kg/m3

  • Density of nuclear matter is independent of the mass number.
Mass Defect ∆m = [Zmp + (A – Z)mn – M] Z = atomic number
mp = mass of proton
A = atomic mass
mn = mass of neutron
M = mass of nucleus
Binding Energy ∆Eb = ∆mc2
or
∆Eb = ∆m × 931.5 MeV		 ∆m = mass defect
  • Binding energy is the minimum energy required to break the nucleus into its constituent particles.

Some Important Concepts

Term Definition / Explanation
Composition of Nucleus
  • The atomic nucleus consists of two types of elementary particles i.e., protons and neutrons, protons and neutrons are collectively known as nucleons.

  • Atomic number = Number of protons (Z)

  • Mass number (A) = Number of protons (Z) + Number of neutrons (N)

  • Nuclear mass is the total mass of the protons and neutrons measured in amu, 1 atomic mass unit (u) = 931.5 MeV/c2
Nuclear Fission
  • Fusing two or more lighter nuclei to a single heavy nucleus is known as nuclear fusion.

  • Fusion reactions take place in stars and Hydrogen bomb.