Thermal Properties of Matter Class 11 Notes Physics Chapter 11
→ 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 = lo α Δθ
→ Change in area is given by
Δ S = So β Δθ.
→ Change in volume is given by
ΔV = Vo Y Δθ.
lt = lo(1 + α Δθ).
St = So (1 + β Δθ).
Vt = Vo (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
To = \(\frac{\mathbf{K}_{1} \mathrm{~d}_{2} \theta_{1}+\mathrm{K}_{2} \mathrm{~d}_{1} \theta_{2}}{\mathbf{K}_{2} \mathrm{~d}_{1}+\mathrm{K}_{1} \mathrm{~d}_{2}}\)
and
To = \(\frac{\mathrm{K}_{1} \theta_{1}+\mathrm{K}_{2} \theta_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}\) 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 tc is
T = tc + 273.15.
→ Resistance varies with temperature as:
Rt = Ro(l + α Δθ)
where Ro = resistance at 0°C
Rt = 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.
→ TK = Tc + 273.15