Mercury
Thermometer: from
-30˚C to 350˚C
Constant
volume gas thermometer: from -200˚C to 500˚C (with H₂), below -200˚C upto -268˚C (with He)
above 1000˚C upto 1600˚C (with N₂ gas and bulb of glazed porcelain)
Platinum
resistance thermometer: form -200˚C to 1200˚C
Thermocouple thermometer: form -200˚C to 1600˚C
Total
Radiation Pyrometer
When
a body is at high temperature, it glows brightly and the radiation emitted by
the body is directly proportional to the fourth power of absolute temperature
of the body. Radiation pyrometer measures the temperature of a body by
measuring the radiation emitted by the body.
This
thermometer is not put in contact with the body. But it cannot measure
temperature below 800˚C because at low temperature emission of radiation is
very small and cannot be detected.
Specific
Heat Capacity:
Specific heat capacity of a material is the amount of heat required to raise
the temperature of unit mass of substance through 1˚. Its SI unit is Joule/
gram˚C.
1
calorie / gram˚C = 4200 Joule / kg Kelvin.
Thermal
Expansion
When
a body is heated its length, surface area and volume increase. The increase in
length , area and volume with the increase in temperature are measured in terms
of coefficient of linear expansion or linear expansively (α) coefficient of
superficial expansion or superficial expansively (β) and coefficient of cubical
expansion or cubical expansively (γ).
Specific
Heat Capacities of different materials (J/kg K)
Water
4200
Ice
2100
Iron 460
K.
Oil 210
Mercury
140
Lead
130
Relation
between α, β and γ.
α:
β :γ =1:2:3
or, β=2 α and γ =3α
