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.

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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.
    Two wires of the same material and the same radius have their lengths in the ratio 2:3. They are connected in parallel to a battery which supplies a current of 15 A. Find the current through the wires.


      • 2.
        Figure shows variation of Coulomb force (F) acting between two point charges with \( \frac{1}{r^2} \), \( r \) being the separation between the two charges \( (q_1, q_2) \) and \( (q_2, q_3) \). If \( q_2 \) is positive and least in magnitude, then the magnitudes of \( q_1, q_2 \), and \( q_3 \) are such that:
        variation of Coulomb force

          • \( q_2<q_1<q_3 \)
          • \( q_3<q_1<q_2 \)
          • \( q_1<q_2<q_3 \)
          • \( q_2<q_3<q_1 \)

        • 3.
          Two coils ‘1’ and ‘2’ are placed close to each other as shown in the figure. Find the direction of induced current in coil ‘1’ in each of the following situations, justifying your answers:
          Two coils ‘1’ and ‘2’ are placed

          (a) Coil ‘2’ is moving towards coil ‘1’.
          (b) Coil ‘2’ is moving away from coil ‘1’.
          (c) The resistance connected with coil ‘2’ is increased keeping both the coils stationary.


            • 4.

              A circular coil of diameter 15 mm having 300 turns is placed in a magnetic field of 30 mT such that the plane of the coil is perpendicular to the direction of the magnetic field. The magnetic field is reduced uniformly to zero in 20 ms and again increased uniformly to 30 mT in 40 ms. If the EMFs induced in the two time intervals are \( e_1 \) and \( e_2 \) respectively, then the value of \( e_1 / e_2 \) is:

                • 1
                • 2

                • 3

                • 4

              • 5.
                A conductor of length \( l \) is connected across an ideal cell of emf E. Keeping the cell connected, the length of the conductor is increased to \( 2l \) by gradually stretching it. If R and \( R' \) are initial and final values of resistance and \( v_d \) and \( v_d' \) are initial and final values of drift velocity, find the relation between:
                \( R' \) and \( R \)
                \( R' = 4R \)


                  • 6.

                    A battery of emf \( E \) and internal resistance \( r \) is connected to a rheostat. When a current of 2A is drawn from the battery, the potential difference across the rheostat is 5V. The potential difference becomes 4V when a current of 4A is drawn from the battery. Calculate the value of \( E \) and \( r \).

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