Measurement of temperature is called Thermometry Physics.
Temperature is the thermal condition of the body which determines the direction of flow of heat, hence we can say the degree of hotness or coldness is known as temperature.
One of the fixed points in the freezing points of water is known as ice point or lower point.
The other fixed point is the boiling point of water and known as steam point or upper point.
A Thermometer may be Graduated in following Scales :
- The upper and lower points of Centigrade scale are 100°C and 0°C and the fundamental interval is 100°C.
- The upper and lower points of Fahrenheit scale are 212°F and 32°F and fundamental interval is 180°.
- The upper and lower points of Reaumur scale are 80°R and 0°R and fundamental interval is 80°.
- The upper and lower points of Kelvin scale are 373 K and 273 K and the fundamental interval is 100°.
- The upper and lower points of Rankine scale are 672°Ra and 460°Ra and the fundamental interval is 212°.
Relation between different Temperature Scales :
C / 100 = F – 32 / 180 = R / 80
C/100= K – 273 / 100 = Ra – 460 / 212
The exact value of absolute zero is 273. 16K.
Triple Points of Water
A substance is found to exist in three states : solid, liquid and gas.
For each substance there is a set of temperatures and pressures at which any two of the three states of the substance may coexist in equilibrium.
This temperature is called triple point of the substance.
Triple point of water has coordinates 0.0075°C temperature and 4.58 mm pressure.
- The temperature at which centigrade and Fahrenheit thermometers read the same is -40°C. The temperature at which Fahrenheit and Kelvin scale read the same is 574.25.
- The temperature at which Fahrenheit and Reaumur scale read the same is -25.6.
- The temperature at which Celsius and Reaumur scale read the same is zero.