Emissivity is defined as the ratio of the energy radiated from a material's surface to that radiated from a perfect black body at the same temperature and wavelength.

Prevost theory states that all bodies emit thermal radiation at all temperatures above absolute zero irrespective of the nature of the surroundings

The state at which temperature attains constant value everywhere and there is no further transfer of heat anywhere is called steady state.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid and solid) of that substance coexist in thermodynamic equilibrium. The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid and solid) of that substance coexist in thermodynamic equilibrium.

The latent heat for a solid - gas state change is called the latent heat of sublimation (Ls)

The latent heat for a liquid -gas state change is called the latent heat of vaporization (L_v)

Temperature of sin x = 100°C + 273 = 373 K
Temperature of sin x = 300°C + 273 = 573 K
Efficiency \(\eta \) = ?
\(\eta =1-\cfrac { 273 }{ 573 } \)
\(=\cfrac { 537-273 }{ 573 } =\cfrac { 300 }{ 573 } =52.3%\)
(a) By decreasing the cold reservoir
\(\eta =1-\cfrac { { T }_{ 2 } }{ { T }_{ 1 } } \)
T₂ = 50 + 273 = 323 k
T₁= 300 + 273 = 573 k
\(\eta =1-\cfrac { 523 }{ 573 } =\cfrac { 573-323 }{ 573 } \)
= 0.436\(\times\)100
= 43.6%
(b) By increasing the temperature of hot reservoir
T₁ = 350 + 273 = 623 k
T_{2 =}100+273=373k
\(\eta =1-\cfrac { { T }_{ 2 } }{ { T }_{ 1 } } =1-\cfrac { 373 }{ 623 } =\cfrac { 623-373 }{ 623 } \)
= 0.401\(\times\)100
=40.1%
Method (a) is more efficient than method (b).

Heat energy supplied to the gas Q = 6\(\times\)10⁵J
Change in Volume\(\triangle \)V = (6 - 4) = 2m³
(a). Atmospheric pressure \(P=1.013 \times 10^{5} \mathrm{Nm}^{-2}\)
\(\Delta V =2 \mathrm{~m}^{3} \)
\(\therefore \text {Work done by the gas } =1.013 \times 10^{5} \times 2  \)
\(=2.026 \times 10^{5} \mathrm{~J}  \)
\(\mathrm{~W} =202.6 \mathrm{~kJ}\)
(b) Change in internal energy = ΔU
\(\Delta U =\Delta Q-\Delta W=\Delta Q-P \Delta V  \)
\(=6 \times 10^{5}-2.026 \times 10^{5}  \)
\(=3.974 \times 10^{3} \mathrm{~J}  \)
\(\Delta U =3.97 \mathrm{~kJ}\)
(c)

Two systems are said to be in thermal equilibrium with each other if they are at the same temperature, will not change with time.

The different types of thermodynamic system are
(i) open system
(ii) closed system
(iii) isolated system

Wien's law states that, the wavelength of maximum intensity of emission of a black body radiation is inversely proportional to the absolute temperature of the black body.
\({ \lambda }_{ m } \)∝\(\frac { 1 }{ T } \) 
\({ \lambda }_{ m }=\frac { b }{ T } \)

(a) Work done by the gas along AB
W = P\(\triangle \)V
∴ W = 600\(\times\)3 = 1800 J = 1.8 kJ
(b) Work is done on the gas along BC 
W = -P\(\triangle \)V
= -400\(\times\)(6 - 3)
= - 400 x 3 = -1200 J
=-1.2 kJ
(c) Net work done in the process
= Area under the curve AB
= Area of rectangle + Area of triangle
Area of triangle =\(\cfrac { 1 }{ 2 } \)\(\times\)b\(\times\) h
\(=\cfrac { 1 }{ 2 } \times \triangle V\times \triangle P\)
=\(\cfrac { 1 }{ 2 } \)\(\times\)3\(\times\)200 = 300J
Area of rectangle = I\(\times\) b
=400\(\times\)3 = 1200 J
∴ Net work done= 1200 + 300
W = 1500 J = 1.5 J
∴ W = 1.5 J

A thermodynamic system is a finite part of the universe. It is a collection of large number of particles (atoms and molecules) specified by certain parameters called pressure (P), Volume  (V) and Temperature (T).

A black body is the one which absorbs completely heat radiations of all wavelengths when heated. A black body neither reflects nor transmits any radiation. Its absorptive power is unity.

The quantity of heat transferred through a unit length of a material in a direction normal to unit surface area due to a unit temperature difference under steady state conditions is known as thermal conductivity of a material.