Heat is a form of energy which produces the sensation of warmth. It is total thermal energy of the body which is sum of kinetic energies of all the individual molecules of the body. It is transferred from one body to the other on account of temperature difference between two bodies. Joule found that when' mechanical work (W) is converted into heat (Q), then the ratio of Wand Q is always constant, represented by J i.e., Joule's mechanical equivalent of heat.
\(J=\frac{W}{Q} \text { or } W=J Q\) 
A measure of temperature is obtained using a thermometer that use Physical Properties which change uniformly with temperature, for example, in common liquid in glass thermometers, mercury, alcohol etc are used whose volume varies linearly with temperature over a wide range.
(i) Define temperature and its significance.
(ii) Define One calorie.
(iii) How does a thermometer work?
(iv) Name the two convenient fixed reference point for measuring temperature.
(v) How celsius temperature and Fahrenheit scale are related to each other?
(vi) What is absolute zero temperature?
(vii) What is Kelvin scale? How it is related with celsius scale?

When solid is heated, the amplitude of vibration of atoms and molecules increases. Therefore effective interatomic separation increases and cause thermal expansion. Thermal expansion of solids are of three types:
(i) Linear expansion
(ii) Area expansion
(iii) Volume expansion. Thermal expansion of liquid are of two kinds. Real expansion and apparent expansion that occurs in form of volume expansion. Thermal expansion of water is anomalous i.e., volume of given amount of water first decreases with increase in temperature from 0 °C to 4 °C and beyond 4 °C volume of water increases with rise of temperature. In thermal expansion of gases is more than solid and liquid but coefficient of volume expansion is dependent on temperature for gases.
(i) On what factors does the coefficient of thermal expansion depend? Write its S.I. unit.
(ii) Write the relation between the three coefficients of expansion \(\alpha, \beta\) and \(\gamma\) for solid.
(iii) A body at higher temperature contains more heat. Comment.
(iv) Why are clock pendulums usually made of invar?
(v) Draw graphical variation of volume and temperature for water.
(vi) How is coefficient of thermal expansion of gases related to temperature?
(vii) State water equivalent.

States of matter viz: solid, liquid and gas are function of temperature and heat content. During the change of state of a substance, the exchange of heat takes place between the substance and surrounding. In this process temperature of substance remains constant. At certain temperature known as melting point. Both the solid and liquid states of the substance coexist in thermal equilibrium. Similarly, at boiling point both the liquid and vapour states of the substance co-exist in the thermal equilibrium. There are certain substance which on heating directly pass from solid to vapour state without passing through the liquid state. This is sublimation process in which solid changes to vapour state of the substance. Process of change of state depends on pressure and temperature.
(i) Define triple point.
(ii) Define latent heat of a substance. 
(iii) What is principle of calorimetry?
(iv) What is effect of pressure on the melting point of a substance?
(v) State phenomenon of relegation.
(vi) What is boiling point? What is effect of pressure on the boiling point?
(vii) What is sublimation?

Three cylindrical rods A, Band C of equal lengths and equal diameters are joined in series as shown in the figure. Their thermal conductivities are 2K, K and 0.5 K respectively.
100°C \(\begin{array}{|l|l|l|} \hline \mathrm{A} & \mathrm{B} & \mathrm{C} \\ \hline \end{array}\) 0°C
In the steady-state, the free ends of rods A and C are at 100 °C and a 0°C respectively. Neglecting loss of heat from the curved surfaces of rods.
(i) Determine the temperature of the junction between rods A and B.
(ii) Determine the temperature of the junction between rods Band C.
(iii) Determine the equivalent thermal conductivity of the combination.
(iv) Define coefficient of thermal conductivity of a solid. Write its S.I unit.
Two rods A and B are of equal length. Each rod has the ends at temperature T₁ and T₂ What is the condition that will ensure equal rates of flow of heat through the rods A and B?

All bodies emit heat energy from their surface by virtue of their temperature. This heat energy is called radiant energy or thermal radiation. The heat that we receive from the sun is transferred to us by a process which, unlike conduction and convection, does not require the help of a medium in intervening space which is almost free of particles. Radiant energy travels in space as electromagnetic waves in the infra-red region of electromagnetic spectrum. They exhibit the phenomenon of interference, diffraction, and polarization as light does.
The emission of radiation from a hot body is expressed in terms of that emitted from a reference body (called the black body) at the same temperature. A black body absorbs and emits radiations of all wavelengths. The total energy E emitted by a unit area of a black body per second is given by E = \(\sigma T^{4}\) 
Where T - is absolute temperature of the body and a is Stefan's constant, if the body is not the perfect black body, then E = \(\varepsilon \sigma T^{4}\) , where \(\varepsilon\) is the emissivity of the body.
(i) Determine the dimensions of Stefan's constant a from Stefan - Boltzman law.
(ii) What is S.I unit of Stefan's constant?
(iii) In which region of the electromagnetic spectrum do thermal radiation lie?
(iv) Which device is used to detect thermal radiation?
(v) When a body A at a higher temperature T₁ is surrounded by another body B at a lower temperature T₂. Write the relation between the rate of loss of heat from body A and temperature.
(vi) On what factor does the rate at which energy is radiated by a body depends?
(vii) On which parameter does the colour of a star depends upon?