Chapter 12 Thermodynamics

ZEROTH LAW OF THERMODYNAMICS

This law states that ‘two systems in thermal equilibrium with a third system are in thermal equilibrium with each other.

THE FIRST LAW OF THERMODYNAMICS

It is the general law of conservation energy applied to any system in which energy transfer from or to the surroundings (through heat and work) is taken into account.

THE SECOND LAW OF THERMODYNAMICS

It states:

Kelvin-Planck statement: No process is possible whose sole result is the absorption of heat from a reservoir and complete conversion of heat into work.

Clausius statement: No process is possible whose sole result is the transfer of heat from a colder object to a hotter object.

It implies that no heat engine can have efficiency equal to 1 or no refrigerator can have co-efficient of performance equal to infinity.

A process is reversible if it can be reversed such that both the system and the surroundings return to their original states, with no change anywhere else in the universe. Spontaneous processes of nature are irreversible.

CARNOT’S ENGINE

Carnot’s engine is a reversible engine operating between two temperatures T₁ (source) and T₂ (sink). The Carnot cycle consists of two isothermal processes connected by two adiabatic processes.

No engine operating between two temperatures can have efficiency greater than that of a Carnot engine.

If Q > 0, heat is added to the system

If Q < 0, heat is removed from the system

If W > 0, work is done by the system

If W < 0, work is done by the system

 Chapter 10 Mechanical Properties Of Fluids

PRESSURE

Pressure is defined as the normal force acting per unit area.

                                           P = F/A

Pressure is a scalar quantity.

PASCAL’S LAW

Pascal’s law states that pressure in a fluid at rest is same at all points which are at the same height.

The pressure in a fluid varies with depth h according to the expression:

                                    P = P₀ + ρgh, where ρ is the density of the liquid

BERNOULLI’S PRINCIPLE

It states that as we move along a streamline, the sum of the pressure and the kinetic energy per unit volume remains constant.

SURFACE TENSION

Surface tension is a force per unit length (or surface energy per unit area) acting in the plane of interface between the liquid and the bounding surface.

    Chapter 9 Mechanical Properties Of Solids

ELASTICITY

Elasticity is a property by the virtue of which the solid regains its original shape once the external force is removed.

PLASTICITY

Plasticity is the property by virtue of which the sold does not regain its original shape even after all the external forces are removed.

DUCTILITY

Ductility is the property of a solid to be drawn into thin wires.

MALLEABILITY

Malleability is the property of a solid to be beaten into thin sheets.

STRESS

Stress is the restoring force per unit area. When we apply an external force on the body to change its shape there is a restoring force that develops in the body in the opposite direction.

Mathematically, Stress = F / A, where F is the restoring force that develops in the body and A is the area. The SI unit of stress is N/m² or Pascal (Pa).

Types of stress:

• Longitudinal stress: It is defined as the restoring force per unit area when the force is applied to the cross sectional area of the cylindrical body. There are two types of longitudinal stress:
  • Tensile stress: When the stress leads to an increase in the length of the body.
  • Compressive stress: When the force applied compresses the body.
• Shearing stress: Also known as tangential stress. The restoring force per unit area when the force is applied parallel to the cross sectional area of the body.
• Hydraulic stress: The restoring force per unit area when the force on the body is applied by a fluid.

STRAIN

Strain is a measure of deformation i.e. the displacement between the particles in the body.

Mathematically, Strain= (Change in length)/ (original length)

Types of strain:

• Longitudinal strain: When the change in length occurs due to longitudinal stress.
• Shearing strain: The relative displacement of the opposite faces of the body as a result of shearing stress.
• Volume strain: The ratio of change in volume to the original volume due to hydraulic stress.

HOOKE’S LAW

This law states that within the elastic limit, stress developed is directly proportional to the strain produced in a body.

Mathematically,

          Stress = k x strain, where k is the modulus of elasticity

Elastic modulus: It is the ratio of stress and strain.