RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids

These comprehensive RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids will give a brief overview of all the concepts.

Rajasthan Board RBSE Solutions for Class 11 Physics in Hindi Medium & English Medium are part of RBSE Solutions for Class 11. Students can also read RBSE Class 11 Physics Important Questions for exam preparation. Students can also go through RBSE Class 11 Physics Notes to understand and remember the concepts easily.

RBSE Class 11 Physics Chapter 9 Notes Mechanical Properties of Solids

→ The property of the material of a body, due to which it regains its original size and shape after the removal of the deforming force, is called elasticity.

→ No body is perfectly elastic or perfectly plastic. All the bodies that are found in nature lie between these two limits.

→ Stress is the restoring force per unit area.

→ There are three types of stress, namely ;

  • Normal stress (tensile stress and compressive stress)
  • Bulk stress/volumetric stress/hydraulic stress,
  • Shearing stress/tangential stress.

→ Strain is defined as the fractional change in dimensions.

RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids 

→ There are three types of strain, namely:

  • Longitudinal strain
  • Volumetric strain
  • Shearing strain

→ Hooke’s law states that;
“ Stress is directly proportional to strain, with in the elastic limit.”
Thus under the elastic limit,
Stress ∝ Strain
\(\frac{\text { Stress }}{\text { Strain }}\) = constant
The constant of proportionality is called as the ‘modulus of elasticity’ or ‘coefficient of elasticity’.

→ Three elastic moduli are used to describe the elastic behaviour of the objects, which are as follows:

  • Young’s modulus
  • Bulk modulus
  • Shear modulus

→ Elastometers which are a class of solids, do not obey Hooke’s law.

→ Stress = \(\frac{\text { Restoring force }}{\text { Area }}\)
The SI unit of stress is Nm-2 and the C.G.S. unit is dyne cm-2. The dimensional formula of stress is [ML-1T-2]

→ Strain = \(\frac{\text { Changeindimension }}{\text { Originaldimension }}\)

→ Modulus of elasticity, E = \(\frac{\text { Stress }}{\text { Strain }}\)
The SI unit of modulus of elasticity is Nm-2 and its dimensions are [ML-1T-2].

→ Young’s modulus of elasticity:
Y = \(\frac{\text { Normal stress }}{\text { Longitudinal strain }}=\frac{F / A}{\Delta L / L}=\frac{F L}{A \Delta L}\)

The SI unit of Young’s modulus of elasticity is Nm-2 or pascal (Pa) and its CGS unit is dyne cm-2
The dimensional formula is [ML-1T-2].

→ Bulk modulus, K = \(\frac{\text { Volumetric stress }}{\text { Volumetric strain }}=-\frac{F / A}{\Delta V / V} K = -\frac{F V}{A \Delta V}\)
The negative sign in the above formula indicates that the volume decreases with the increase in stress. The SI unit is Nm-2 or pascal (Pa) and CGS unit is dyne cm-2.
Its dimensional formula is given as [ML-1T-2].

RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids

→ Shear modulus,
η = \(\frac{\text { Tangential stress }}{\text { Shear strain }}=\frac{F / A}{\theta}=\frac{F}{A \theta}\)
where, [θ = \(\frac{\Delta x}{L}\)]
The SI unit is Nm-2 and its CGS unit is dyne cm-2. The dimensional formula is [ML-1T-2].

→ Poisson's ratio, σ = \(\frac{\text { Lateral strain }}{\text { Longitudinal strain }}\)
= \(\frac{-\Delta D / D}{\Delta L / L}=-\frac{L \cdot \Delta D}{D \cdot \Delta L}\)
The negative sign in the formula indicates that longitudinal and lateral strains are opposite. It has no units and dimensions.

→ Deforming force:
A force which when applied changes the shape or size of the body is called a deforming force.

→ Elasticity:
It is the property of a body due to which it regains its original shape and size back after removing the deforming force, is called elasticity.

→ Plasticity:
The property of a body in which it does not regain its original shape and size back even after the removal of the deforming force, is called plasticity.

→ Stress:
The restoring force per unit area is defined as stress.

→ Normal stress:
The restoring force per unit area normal to the surface of a body is called as normal stress.

→ Tensile stress:
It is defined as the restoring force per unit area in reference to the increase in length (or elongation) of the body.

→ Compressive stress:
It is defined as the restoring force per unit area in case of decrease in length (or contraction) of the body.

RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids

→ Tangential shearing stress:
It is defined as the restoring force per unit area developed due to tangentially applied deforming force.

→ Strain:
Strain is defined as the ratio of the change in any dimension produced in the body to the original dimension.

→ Longitudinal strain:
When deforming force is applied on a body, the ratio of increase in length per unit original length is called the longitudinal strain.

→ Volumetric strain:
When deforming force is applied on a body, the change in volume per unit original volume is defined as volumetric strain.

→ Shear strain:
It is defined as the angle 0 (in radian) through which a face originally perpendicular to the fixed face gets turned on applying tangential deforming force.

→ Ductile materials:
Those materials which show large amount of plastic deformation between the elastic limit and the breaking point are called ductile materials.

→ Brittle materials:
Brittle materials show small amount of plastic deformation between the elastic limit and the breaking point.

→ Elastometers:
Elastometers are those materials for which the strain and stress variation in non linear or not a straight line with the limits of elasticity.

RBSE Class 11 Physics Notes Chapter 9 Mechanical Properties of Solids

→ Modulus of elasticity:
The ratio of stress to strain is defined as the modulus of elasticity.

→ Compressibility:
Compressibility is defined as the reciprocal of bulk modulus of elasticity.

→ Modulus of rigidity:
The ratio of shearing (tangential) stress to shear strain is defined as modulus of rigidity.

→ Elasticity after effect:
The temporary delay caused in regaining the original size and shape by the body, when the deforming force is removed, is termed as the elastic after effect.

→ Elastic fatigue:
Elastic fatigue is defined as the property of a body due to which it loses the strength of being elastic under the influence of repeated alternating forces.

→ Elastic hysteresis:
It is defined as the lagging of strain behind the stress, when a deforming force is applied.

→ Elastic potential energy:
Potential energy stored as a result of deformation of an elastic object; is defined as the elastic potential energy.

Prasanna
Last Updated on Oct. 14, 2022, 5:40 p.m.
Published Oct. 14, 2022