Nuclei Class 12 Notes Physics Chapter 13 - CBSE

Chapter : 13

What are Nuclei ?

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    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.