Heat

• Heat is the form of energy which stimulates our sense organs so that we feel hot or cold.
• Sum of kinetic energies present in each molecules of a body.
• It flows from higher temperature to a body at lower temperature.
• SI unit of Heat is Joule and measured by Calorimeter

Temperature

• Degree of hotness or coldness of a body.
• Average kinetic energy present in each molecules.
• It is the reason for transfer of heat.

Thermometry

• The science of temperature and its measurement.
• Instrument use in thermometry is Thermometer.
• Different Thermometer use analysis of different properties of matter to analyze temperature.

Thermometer:

• Use to measure temperature.
• Lower fixed point: Temperature at which pure ice melts at normal pressure
• Upper fixed point: Temperature at which pure water boils at normal pressure

Types of thermometer

Liquid Thermometer:

Based on expansion of liquid on heating

Its types are:

Mercury Thermometer:

Mercury is used in thermometer due to

• low specific heat capacity
• high thermal conductivity
• uniform expansion over wide range
• can measure -39$°$ C to 357$°$C
• does not stick on the wall of tube
• shinning in nature

Alcohol Thermometer:

It is used in cold region and high mountain where it can measure -117$°$C to 78$°$C

Gas thermometer

• based on change in pressure at constant volume which is directly proportional to change in temperature.
• most sensitive thermometer
• Can measure -268$°$C to 1500$°$C
• 'He' gas is used
• $\frac{t-{\theta }_1}{{\theta }_2-{\theta }_1}=\frac{P_t-P_{{\theta }_1}}{P_{{\theta }_2}-P_{{\theta }_1}}$ where $P_t$= pressure at t$°$C

Resistance thermometer

• Based on variation of resistance of conductor with temperature by $R_{\theta }=R_o(1+\alpha \Delta \theta )$
• Pure platinum is used due to it's high value of temperature coefficient
• can measure 270 $°$C to 700$°$C.

Thermo-electric thermometer

• based on the principle of thermo-electricity (i.e. production of thermo-emf in a thermocouple when the two junctions are at different temperature)
• Temperature Range of -270$°$C to 2300$°$C

Radiation Thermometer

• based on quantity of heat radiation emitted by a body
• also called Pyrometer.
• Measurement of high temperature

vapour pressure thermometer

• Based on the principle of change of vapor pressure with change in temperature
• Measure low temperature
• eg. helium vapor pressure thermometer