Celsius Scale In this scale of temperature, the melting point ice is taken as 0°C and the boiling point of water as 100°C and space between these two points is divided into 100 equal parts

2. Fahrenheit Scale In this scale of temperature, the melt point of ice is taken as 32°F and the boiling point of water as 211 and the space between these two points is divided into 180 equal parts.

3. Kelvin Scale In this scale of temperature, the melting pouxl ice is taken as 273 K and the boiling point of water as 373 K the space between these two points is divided into 100 equal pss

Relation between Different Scales of Temperatures

Thermometric Property

The property of an object which changes with temperature, is call thermometric property.Different thermometric properties thermometers have been given below

(i) Pressure of a Gas at Constant Volume

where p, p₁₀₀. and p_t , are pressure of a gas at constant volume 0°C, 100°C and t°C.

A constant volume gas thermometer can measure tempera from – 200°C to 500°C.

(ii) Electrical Resistance of Metals

Rt = R₀(1 + αt + βt²)

Where α and β are constants for a metal.

As β is too small therefore we can take

Rt = R₀(1 + αt)

where, α = temperature coefficient of resistance and

R0 and Rt

, are electrical resistances at 0°C and t°C.

where R1 and R2 are electrical resistances at temperatures t1 and t2.

where R100 is the resistance at 100°C.

Platinum resistance thermometer can measure temperature from —200°C to 1200°C.

(iii) Length of Mercury Column in a Capillary Tube

l_t = l₀(1 + αt)

where α = coefficient of linear expansion and l0, lt are lengths of mercury column at 0°C and t°C.

Thermo Electro Motive Force

When two junctions of a thermocouple are kept at different temperatures, then a thermo-emf is produced between the junctions, which changes with temperature difference between the junctions. Thermo-emf

E = at + bt²

where a and b are constants for the pair of metals.

Unknown temperature of hot junction when cold junction is at 0°C.

Where E₁₀₀ is the thermo-emf when hot junction is at 100°C.

A thermo-couple thermometer can measure temperature from —200°C to 1600°C.

Thermal Equilibrium

When there is no transfer of heat between two bodies in contact, the the bodies are called in

thermal equilibrium.

Zeroth Law of Thermodynamics

If two bodies A and B are separately in thermal equilibrium with thirtli body C, then bodies A and B will be in thermal equilibrium with each other.

Triple Point of Water

The values of pressure and temperature at which water coexists inequilibrium in all three states of matter, i.e., ice, water and vapour called triple point of water.

Triple point of water is 273 K temperature and 0.46 cm of mere pressure.

Specific Heat

The amount of heat required to raise the temperature of unit mass the substance through 1°C is called its specific heat.

It is denoted by c or s.

Its SI unit is joule/kilogram-°C'(J/kg-°C). Its dimensions is [L2T^-2θ^-1].

The specific heat of water is 4200 J kg-1°C^-1or 1 cal g-1 C^-1

, which high compared with most other substances.

Gases have two types of specific heat

1. The specific heat capacity at constant volume (C_v).

2. The specific heat capacity at constant pressure (C_r).

Specific heat at constant pressure (Cp) is greater than specific heat constant volume (C_V), i.e.,C_p > C_V .

For molar specific heats C_p – C_V = R

where R = gas constant and this relation is called Mayer’s formula.

The ratio of two principal sepecific heats of a gas is represented by γ.

The value of y depends on atomicity of the gas.

Amount of heat energy required to change the temperature of any substance is given by

Q = mcΔt

• where, m = mass of the substance,
• c = specific heat of the substance and
• Δt = change in temperature.