→ Heat is the thermal energy that transfers from a body at a higher temperature to the other body at a lower temperature.

→ Temperature is the property of a body that determines whether or not it is in thermal equilibrium with its surroundings.

→ Thermometry is the branch of heat that deals with the measurement of temperature.

→ S.I. Unit of coefficient of thermal expansion in K^-1.

→ The volume of water decreases with the increase in temperature from 0°C to 4°C. It is called the anomalous expansion of water.

→ The density of water is maximum at 4°C and. its maximum value is 1 g cm^-3 or 10³ kg m^-3.

→ Water (0° to 4°C) and silver iodide (80°C to 141°C) contract on heating.

→ Quartz, pyrex glass, fused silica and invar neither expand nor contract on heating.

→ On a freezing, the volume of ice becomes more than that of water in cold countries when the temperature goes below 0°C and thus the pipe expands and may burst.

→ The principle of Calorimetry is:
Heat gained = Heat lost.

→ A sensitive thermometer is one that shows a large change in the position of mercury meniscus for a small change in temperature.

→ The critical temperature is that temperature up to which gas can be liquified by applying pressure alone.

→ Vapour is a gas above the critical temperature and gas is a vapour below the critical temperature.

→ ΔC = ΔK.

→ In order to convert the temperature from one scale to another, the following relation is used :
\(\frac{\mathrm{C}-0}{100}=\frac{\mathrm{F}-32}{180}=\frac{\mathrm{R}-0}{80}=\frac{\mathrm{K}-273.15}{100}\)

→ Ideal gas equation is PV = nRT.

→ Heat Capacity = mC = W = water equivalent.

→ There are three modes of transfer of heat i.e. conduction, convection and radiation.

→ Radiation mode is the fastest mode of heat transfer.

→ A body that neither reflects nor transmits any heat radiation but absorbs all the radiation is called a perfectly black body.

→ Q = mL
where Q = quantity of heat required for a change from one state to another.
L = Latent heat, m = mass of substance.

→ Melting point is a characteristic of the substance and it also depends 7 on the pressure.

→ Skating is possible on snow due to the formation of water below the skates. It is formed due to the increase of pressure and it acts as a lubricant.

→ The change from solid-state to vapour state without passing through the liquid state is called sublimation and the substance is said to be sublime.

→ Solid CO₂ is called dry ice and it sublimes.

→ During the sublimation process, both the solid and the vapour states of a substance coexist in thermal equilibrium.

→ Melting: The change of state from solid to liquid is called melting.

→ Fusion: The change of state from liquid to solid is called fusion.

→ Melting point: The melting point is the temperature at which the solid and the liquid states of the substance co-exist in thermal equilibrium with each other.

→ Regelation: Regelation is the process of refreezing.

→ Vaporisation: Change of state from liquid to vapour is called vaporisation.

→ Boiling point: Boiling point is the temperature at which the liquid and the vapour states of the substance co-exist in thermal equilibrium with each other.

→ Normal melting point: The melting point of a substance at standard atmospheric pressure is called its normal melting point.

→ Normal boiling point: The boiling point of a substance at standard atmospheric pressure is called its normal boiling point.

Important Formulae:
→ \(\frac{T}{T_{t r}}=\frac{P}{P_{t r}}\)

→ Change in length is given by
Δ l = l_o α Δθ

→ Change in area is given by
Δ S = S_o β Δθ.

→ Change in volume is given by
ΔV = V_o Y Δθ.
l_t = l_o(1 + α Δθ).
S_t = S_o (1 + β Δθ).
V_t = V_o (1 + γ Δθ).
where α, β & γ are called coefficient of linear, superficial and volume expansion respectively.

→ Thermal conductivity of a composite rod made of two conductors. of equal lengths and joined in series is given by
K = \(\frac{2 \mathrm{~K}_{1} \mathrm{~K}_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}\)

→ Temperature of the interface connecting two rods of different lengths d₁ and d₂ is given by
T_o = \(\frac{\mathbf{K}_{1} \mathrm{~d}_{2} \theta_{1}+\mathrm{K}_{2} \mathrm{~d}_{1} \theta_{2}}{\mathbf{K}_{2} \mathrm{~d}_{1}+\mathrm{K}_{1} \mathrm{~d}_{2}}\)
and
T_o = \(\frac{\mathrm{K}_{1} \theta_{1}+\mathrm{K}_{2} \theta_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}\) if their lengths are equal i.e. if d₁ = d₂.

→ If areas of the cross-section are equal, Then
K = \(\frac{\mathrm{K}_{1}+\mathrm{K}_{2}}{2}\)

→ \(\frac{\text { Change in temperature }}{\text { Time }}\) = KΔθ
where Δθ = difference of average temperature and room temperature.

→ Specific heat capacity of a substance is given by
C = \(\frac{\Delta \mathrm{Q}}{\mathrm{M} \Delta \theta}\)
or
ΔQ = MCΔθ.

→ The relation between Kelvin temperature (T) and the celcius temperature t_c is
T = t_c + 273.15.

→ Resistance varies with temperature as:
R_t = R_o(l + α Δθ)
where R_o = resistance at 0°C
R_t = resistance at t°C
α = temperature coefficient of resistance
Δθ = change in temperature.

→ Q = mL, where L = latent heat.

→ Temperature difference Δ°F equivalent to Δ°C is
ΔF = \(\frac{9}{5}\) × ΔC

→ Temperature difference ΔK equivalent to ΔF is
ΔF = \(\frac{9}{5}\)ΔK.

→ T_K = T_c + 273.15