Physics

# 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

### 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 357C
• 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 -117C to 78C

### Gas thermometer

• based on change in pressure at constant volume which is directly proportional to change in temperature.
• most sensitive thermometer
• Can measure -268C to 1500C
• 'He' gas is used
• where = pressure at tC

### Resistance thermometer

• Based on variation of resistance of conductor with temperature by
• Pure platinum is used due to it's high value of temperature coefficient
• can measure 270 C to 700C.

### 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 -270C to 2300C