NCERT Solutions for Class 12 Physics Chapter 13: Nuclei

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NCERT Solutions for class 12 physics chapter 13 Nuclei are given in this article. Atomic Nucleus is the small, dense and central part of the Atom consisting of Protons, which are positively charged and Neutrons, which are electrically neutral containing more than 99.9% of the mass of an atom and are ten thousand times smaller than an atom.

Unit 8 Atoms and Nuclei along with Unit 7 Dual Nature of Radiation and Matter has a weightage of 12 marks in the CBSE Board examinations. NCERT Solutions Class 12 Physics Chapter 13 covers concepts of Mass-Energy and Nuclear Binding EnergyRadioactive Decay, and Nuclear Energy.

Download PDF: NCERT Solutions for Class 12 Physics Chapter 13


NCERT Solutions for Class 12 Physics Chapter 13

The NCERT solutions for class 12 physics chapter 13: Nuclei are given below.

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Class 12 Physics Chapter 13 Nuclei – Topics Covered

  • Atomic Mass Unit (amu): The unit used to express atomic masses is known as the atomic mass unit. It is defined as 1/12th of the mass of a Carbon atom (C12).
1 u = 1.660539 x 10-27 kg
  • Atomic number of an element refers to the number of protons that are present inside the nucleus of an atom of an element.
Atomic number = Number of protons = Number of electrons
  • Mass number of an element refers to the total number of protons and neutrons inside the atomic nucleus of the element.
Mass number = Number of protons + Number of neutrons = Number of electrons + Number of neutrons i.e. A = Z + N
  • Size of Nucleus: If R is the radius of the nucleus that has mass number A, then the size of the nucleus can be represented by:
\({4 \over 3} \pi R^3 \propto A => R \propto A^{1/3} => R = R_0A^{1 \over 3}\)
  • Radioactivity Decay Law: According to the Radioactive Decay law, the rate of decay of radioactive atoms at any instant is directly proportional to the number of atoms present at that instant.
\({dN \over dt} \propto N, {dN \over dt}=\ - \lambda N\)

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CBSE CLASS XII Related Questions

  • 1.
    (a) Consider the so-called ‘D-T reaction’ (Deuterium-Tritium reaction).
    In a thermonuclear fusion reactor, the following nuclear reaction occurs: \[ \ ^{2}_1 \text{H} + \ ^{3}_1 \text{H} \longrightarrow \ ^{4}_2 \text{He} + \ ^{1}_0 \text{n} + Q \] Find the amount of energy released in the reaction.
    % Given data Given:
    \( m\left(^{2}_1 \text{H}\right) = 2.014102 \, \text{u} \)
    \( m\left(^{3}_1 \text{H}\right) = 3.016049 \, \text{u} \)
    \( m\left(^{4}_2 \text{He}\right) = 4.002603 \, \text{u} \)
    \( m\left(^{1}_0 \text{n}\right) = 1.008665 \, \text{u} \)
    \( 1 \, \text{u} = 931 \, \text{MeV}/c^2 \)


      • 2.
        Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).


          • 3.
            The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:

              • \( \frac{\alpha}{r} \)
              • \( \frac{\alpha r^2}{2} \)
              • \( \frac{\alpha}{2r^2} \)
              • \( -\frac{\alpha}{r} \)

            • 4.
              A rectangular glass slab ABCD (refractive index 1.5) is surrounded by a transparent liquid (refractive index 1.25) as shown in the figure. A ray of light is incident on face AB at an angle \(i\) such that it is refracted out grazing the face AD. Find the value of angle \(i\).
              A rectangular glass slab ABCD (refractive index 1.5)


                • 5.
                  A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases. parallel plate capacitor


                    • 6.
                      In the circuit, three ideal cells of e.m.f. \( V \), \( V \), and \( 2V \) are connected to a resistor of resistance \( R \), a capacitor of capacitance \( C \), and another resistor of resistance \( 2R \) as shown in the figure. In the steady state, find (i) the potential difference between P and Q, (ii) the potential difference across capacitor C.
                      potential difference across capacitor C

                        CBSE CLASS XII Previous Year Papers

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