RBSE Class 11 Physics Notes Chapter 12 Thermodynamics

These comprehensive RBSE Class 11 Physics Notes Chapter 12 Thermodynamics will give a brief overview of all the concepts.

RBSE Class 11 Physics Chapter 12 Notes Thermodynamics

→ Thermodynamical system:
An assembly of a very large number of particles having a certain value of pressure, volume and temperature is called a thermodynamical system.

→ Surroundings:
Everything outside the system which can have a direct effect on the system is called its surroundings.

→ Thermal equilibrium:
Two systems are in thermal equilibrium with each other if they have the same temperature.

→ Isothermal process:
A process in which temperature remains constant is called an isothermal process. For such a process,
PV = constant or P₁V₁ = P₂V₂

→ Adiabatic process:
A process in which thermally insulated system neither loss nor gains heat from the surroundings is called adiabatic process.

 

→ Isobaric process:
A process in which volume remains constant is called isobaric process. For such a process
\(\frac{V}{T}\) = constant T
or \(\frac{V_1}{T_1}=\frac{V_2}{T_2}\)

→ First Law of Thermodynamics:
It states that if heat dQ is given to a system, a part of it is used in increasing the internal energy by an amount dU and the remaining energy used in doing the external work dW. It is just a statement of the law of conservation of energy. Thus
dQ = dU + dW
or dQ = dU + PdV

→ Work done in an isothermal process:
Work done when 1 mole of a gas expands isothermally,
W_iso = 2.303 RTlog\(\frac{V_2}{V_1}\) = 2.303 log\(\frac{P_2}{P_1}\)

→ Work done in an adiabatic process:
Work done when 1 mole of a gas expands adiabatically and its temperature falls from T₁ to T₂.
W_adia = \(\frac{R}{\gamma-1}\)[T₁ - T₂]
= \(\frac{1}{\gamma-1}\)[P₁V₁ - P₂V₂]

→ Molar specific heat of a gas at constant volume:
It is defined as the amount of heat required to raise the temperature through 1°C of one mole of gas at constant volume.

→ Molar specific heat of a gas at constant pressure:
It is defined as the amount of heat required to raise the temperature through a 1°C of one mole of gas at constant pressure.

→ Heat engine:
It is a device which converts continuously heat energy into mechanical energy in a cyclic process.

→ Efficiency of a heat engine:
It is the ratio of useful work done (W) by the engine per cycle to the heat energy (Qi) absorbed from the source per cycle.
η = \(\frac{\text { Work output }}{\text { Heatinput }}=\frac{W}{Q_1}=\frac{Q_1-Q_2}{Q_1}=1-\frac{Q_2}{Q_1}\)

→ Second law of Thermodynamics:
It is impossible for a self acting machine, unaided by external agency, to transfer heat from a body to another at higher temperature.

→ Carnot’s heat engine:
It is an ideal heat engine which is based on Carnot’s reversible cycle. Its working consists of four steps viz. isothermal expansion, adiabatic expansion, isothermal compression and adiabatic compression. The efficiency of Carnot’s engine is given by,
η = 1 - \(\frac{Q_2}{Q_1}\) = 1 - \(\frac{T_2}{T_1}\)
Where T₁ and T₂ are the temperatures of source and sink respectively.

→ Carnot’s Theorem:
It states that no engine working between two given temperatures can have efficiency greater than that of the Carnot’s engine working between the same two temperatures.

→ Equivalence between heat and work
W = JQ or J = \(\frac{W}{Q}\)

→ Work done during change in volume from V₁ to V₂
W = \(\int_{V_1}^{V_2}\)PdV

→ Work done during cyclic process = Area of closed curve
For clockwise process W is + ve.
For anticlockwise process W is - ve.

→ First Law of Thermodynamics,
dQ = dU + dW

→ Specific heat, s = \(\frac{d Q}{m d T}\)

→ Change in internal energy dU = U_f - U_i

→ Molar specific heat
C_V = \(\left(\frac{d Q}{d T^2}\right)_V\) and C_P = \(\left(\frac{d Q}{d T}\right)_P\)
and \(\frac{C_P}{C_V}\) = γ

→ Mayer’s relation: C_P - C_V = R

→ In isothermal process. PV = constant

→ Work done in isothermal process
W = 2.303 μRT log10 \(\left(\frac{V_2}{V_1}\right)\)
and W = 2.303 μRTlog10 \(\left(\frac{P_2}{P_1}\right)\)

→ Work done in isobaric process: W = μH(T₂ - T₁)

→ In adiabatic process
(i) PV^γ = constant = K
\(\frac{T^\gamma}{P^{\gamma-1}}\) = K and
TV^γ-1 = K

→ Work done in adiabatic process
W = \(\frac{\mu R}{\gamma-1}\)(T₁ - T₂)
and W = \(\frac{1}{(\gamma-1)}\)(P₁V₁ - P₂V₂)

→ Efficiency of Carnot’s engine
η = 1 - \(\frac{T_2}{T_1}\)

→ Coefficient of performance
β = \(\frac{T_2}{T_1-T_2}\)

→ Equation of State:
The mathematical relation between the pressure, volume and temperature of a thermodynamical system.

→ State Variables:
The macroscopic quantities which are used to describe the equilibrium states of a thermodynamic system are called state variables.

→ Internal energy:
The internal energy of a system is the sum of kinetic and potential energies of molecules.

→ Quasi-static process:
A quasi-static process is an infinitely slow process such that system remains in thermal and mechanical equilibrium with the surroundings throughout.

→ Cyclic process:
Any process in which the system returns to its initial state after undergoing a series of changes known as a cyclic process.

→ Heat engine:
It is a device which converts continuously heat energy into mechanical energy in a cyclic process.