HEAT AND TEMPERATURE Notes

Heat and temperature

   Heat is a form of energy that follows from a body of higher temperature to one of lower temperature. Temperature is the degree of hotness or coldness of a body.

 Thermometry:
     The science of temperature and its measurement is called thermometry.

 Scales of thermometer:

There are different temperature scales thermometers in use. They are as;

1.     Celsius scale: In this scale, the lower fixed point is marked as o and the upper fixed point marked as 1oo. The interval between the two fixed points is divided into 100 equal parts. Each part or degree represents 1^oC.

2.     Fahrenheit scale: In this scale, the lower fixed point is marked as 32 and the upper fixed point is marked as 212. The interval between the two fixed points is divided into 180 equal parts. Each part or degree represents 1^o F.

3.     Reaumur scale: In this scale, the lower fixed point is marked as 0 and the upper fixed point is marked as 80. The interval between the two fixed points is divided into 80 equal parts. Each part or degree represents 1^oR.

4.      Absolute temperature scale: In this scale, the lower fixed point is marked as 237K and the upper fixed point is marked as 373K. The interval between the two fixed points is divided into 100 equal parts. Each part or division represents 1K.

 

Zeroth law of thermodynamics:
     When a hot substance is placed in contact with a cold substance, heat flows from hot to cold substances. Finally, the heat flow ceases and both attain the same temperature.

     The bodies are then said to be the thermal equilibrium.
     Two systems are said to be thermal equilibrium if they have the same temperature.

Absolute scale of temperature:
       Absolute temperature scale: It is used to measure the temperature. Using an absolute temperature scale we can measure the temperature 273k-373K. In this scale, the lower fixed point is marked as 237K and the upper fixed point is marked as 373K. The interval between the two fixed points is divided into 100 equal parts. Each part or division represents 1K.

Relation between Celsius, Fahrenheit and Kelvin scale of temperature:
        There are two points in all temperatures scales and different intervals between them. If C, F, R and K be the temperature of body in Celsius, Fahrenheit Reaumur and Kelvin scale respectively,
Then we have,
    (C - 0) / (100 - 0) = (F -32) / (212 - 32) = (R - 0) / (80 - 0) = (K - 273) / (373 - 273)