NCERT Solutions for class 11 Physics Chapter 9: Mechanical properties of solids

NCERT Solutions for Class 11 Physics Chapter 9: Mechanical Properties of Solids are provided in this article below. Mechanical properties of solids define the various characteristics of solids such as their resistance to deformation and their strength. 

Chapter 9 Mechanical Properties of Solids belongs to Unit 7 Properties of Bulk Matter. Unit 7 along with Unit 8 Thermodynamics and Unit 9 Behaviour of Perfect Gases and Kinetic Theory of Gases has a weightage of 20 marks in the Class 11 Examination. The Class 11 NCERT Solutions for Mechanical Properties of Solids discusses concepts such as Elastic behaviour of solidsHooke’s law, and the Stress-strain curve.

Download PDF: NCERT Solutions for Class 11 Physics Chapter 9


NCERT Solutions for Class 11 Physics Chapter 9

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Class 11 Physics Chapter 9 – Concepts Covered

  • Stress is the ratio of the internal force F, produced when a substance is deformed, to the area A over which the force acts. 
\(Stress = {F \over A}\)
  • Strain is the ratio of the change in shape or size to the original shape or size. It is just a number and has no dimensions.
Strain is of 3 types – Longitudinal strain, Volumetric strain, and Shear strain
  • As per Hooke’s law, the ratio of stress to the corresponding strain produced within elastic limits is a constant. This constant is known as the modulus of elasticity. 
\(F_s = -kx\)
  • For a solid, in wire or a thin rod form, Young’s modulus of elasticity is defined as the ratio of longitudinal stress to longitudinal strain within the elastic limit. 

Young's Modulus

  • Poisson’s Ratio – The ratio of change in diameter (ΔD) to the original diameter (D) is known as lateral strain. The ratio of change in length (Δl) to the original length (l) is known as longitudinal strain. The ratio of lateral strain to the longitudinal strain is called Poisson’s ratio.
\(Poisson's\ Ratio\ = {Lateral\ strain \over Longitudinal\ Strain}\)

CBSE CLASS XII Related Questions

  • 1.
    If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.


      • 2.
        Two small identical metallic balls having charges \( q \) and \( -2q \) are kept far at a separation \( r \). They are brought in contact and then separated at distance \( \frac{r}{2} \). Compared to the initial force \( F \), they will now:

          • attract with a force \( \frac{F}{2} \)
          • repel with a force \( \frac{F}{2} \)
          • repel with a force \( F \)
          • attract with a force \( F \)

        • 3.
          If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.


            • 4.
              Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field \( \mathbf{B} \) at a point \( (1 \, \text{m}, 1 \, \text{m}, 0) \).


                • 5.
                  Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))


                    • 6.
                      What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?

                        CBSE CLASS XII Previous Year Papers

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