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NCERT Solutions for Class 11 Physics Ch-8: Mechanical Properties of Solids
NCERT Solutions for Class 11 Physics Chapter 8 Mechanical Properties of Solids covers the concepts of stress, strain, Hooke's law, elastic moduli, and the elastic behaviour of materials under applied forces.
Overview of Topics & Subtopics
Important Questions and Answers
Q1: Define stress and strain, and state their SI units.
Answer: Stress is the internal restoring force developed per unit area of a deformed body, with SI unit N/m² (pascal). Strain is the ratio of change in dimension (length, volume, or shape) to the original dimension, and being a ratio of similar quantities, it has no unit.
Q2: State Hooke's Law.
Answer: Hooke's Law states that, within the elastic limit of a material, the stress developed in the body is directly proportional to the strain produced, i.e., stress = k × strain, where k is a constant of proportionality depending on the material and known as its modulus of elasticity.
Q3: Define Young's modulus of elasticity.
Answer: Young's modulus is defined as the ratio of longitudinal stress to longitudinal strain within the elastic limit of a material, Y = (F/A)/(ΔL/L), and it is a measure of the stiffness of a solid material.
Q4: What is the significance of the elastic limit on a stress-strain curve?
Answer: The elastic limit is the maximum stress up to which a material returns to its original shape and size once the deforming force is removed. Beyond this point, the material undergoes permanent (plastic) deformation and does not fully recover its original dimensions.
Q5: Derive the expression for elastic potential energy stored in a stretched wire.
Answer: The elastic potential energy stored in a stretched wire is given by U = (1/2) × stress × strain × volume = (1/2)F·ΔL, obtained by calculating the work done in gradually stretching the wire against the internal restoring force, which increases linearly with extension according to Hooke's Law.
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