Students can go through AP Inter 1st Year Physics Notes 13th Lesson Thermodynamics will help students in revising the entire concepts quickly.

## AP Inter 1st Year Physics Notes 13th Lesson Thermodynamics

→ Zero law of thermodynamics states that, two systems in thermal equilibrium with a third system seperately are in thermal equilibrium with each other.

→ The zeroth law of thermodynamics led us to the con¬cept of temperature.

→ Reversible process: A process that can be retraced back in the opposite direction in such a way that the system passes through the same states as in the direct process, and finally the system and the surroundings return to their original states, with no other change any wherelse in the Universe is called a reversible process

→ Irreversible process : A process that cannot be retraced back in the opposite direction is called as Irreversible process.

→ Thermodynamics is the branch of Physics dealing with the inter relation between heat and mechanical energy.

→ Thermodynamics is applicable only when the system is T in equilibrium.

→ Temperature is a thermal condition of a substance and d measures its relative hotness.

→ The mathematical representation of zeroth law of thermodynamics f (P, V, T) = 0.

→ The energy transferred by a non-mechanical way is called heat.

→ The mechanical equivalent J is the amount of mechanical work to be done to produce unit quantity of heat.

J = \(\frac{W}{Q}\) its value in CCS system is 4.2 × 10^{7} erg/cal

In S.l. system J is 1.

→ First law of thermodynamics : The heat supplied to the system is equal to the sum of the increase in internal energy of the system and the external work done by the system.

dQ = dU + dW or dQ = dU + PdV

→ First law of thermodynamics is only another statement of the Law of Conservation of Energy.

→ Quasi – static process: An infinitesimally slow process in which at each and every intermediate stage, the system remains in thermal and mechanical equilibrium with the surroundings through out the entire process.

→ Cyclic process : A process in which the system after passing through various states pressure, volume and temperature changes) returns to its initial state is called a cyclic process.

→ In isobaric process the pressure is constant while in isochoric process the volume is constant.

→ Carnot engine is a reversible engine operating between two temperatures T_{1} (source) and T_{2} (sink). The efficiency of a cannot engine is given by

η = 1 – \(\frac{T_2}{T_1}\)

→ C_{p} is always greater than C_{v}.

∴ C_{p} – C_{v} = R and \(\frac{C_p}{C_v}\) = y

For mono atomic gas γ = \(\frac{5}{3}\), for diatomic gas γ = \(\frac{7}{5}\)

For tnatomic gas γ = \(\frac{4}{3}\)

→ Isothermal change: The changes of pressure and volume of a gas at constant temperature with exchange of heat is called isothermal changes.

PV = Constant

→ Workdone by an ideal gas during isothermal process

W = RT log_{e} \(\frac{V_2}{V_1}\) or 2.303 RT log_{10}\(\left[\frac{V_2}{V_1}\right]\)

→ Adiabatic change : The changes in pressure and volume of a gas resulting a change in temperature without exchange of heat in an isolated system is called adiabatic changes.

→ In adiabatic process

\(P_1 V_1^\gamma=P_2 V_2^\gamma, T_1 V_1^{\gamma-1}=T_2 V_2^{\gamma-1}, T_1^\gamma P_1^{1-\gamma}=T_2^\gamma P_2^{1-\gamma}\)

→ Workdone in an adiabatic change W = \(\frac{\mu \mathrm{R}}{\gamma-1}\left(\mathrm{~T}_1-\mathrm{T}_2\right)\)

→ Clausius statement of second law : Heat cannot itself flow from cold body to hot body.

→ Kelvin’s Statement : It is impossible to derive continuous supply of energy in cooling a body below the coldest of its surroundings.

→ Latent heat (L): The quantity of heat absorbed or liberated during the change of state by unit mass of substance, without any change in temperature is called Latent heat.

L = \(\frac{Q}{M}\)

→ Unit of 1′: Joule / kg

Dimension of L : L = \(\frac{Q}{M}\) = [L^{2} T^{-2}]

→ Latent heat of fusion of ice L_{ice} = 80 cal/gm

= 0.335 × 10^{6} J kg^{-1}

Latent heat of steam L_{steam} = 540 cal/gm

= 2.26 × 10^{6} J kg^{-1}