CBSE Class 9: Matter In Our Surroundings - Temperature and Latent Heat

In this video we will learn about the temperature and its units. We will also get to know about the latent heat.

The degree Celsius is the most commonly used unit to measure the temperature. The laboratory thermometer and the clinical thermometer are both calibrated on Celsius scale of temperature.

Even the temperature measured in Kelvin or Degree Fahrenheit can be related to the Degree Celsius value.

• The temperature values in different units can be related as follows:

          a) The relation between Kelvin scale and Celsius scale can be written as:

          Temp. on Kelvin scale = Temp. on Celsius scale + 273

          Absolute zero temperature = 0 K = - 273⁰ C

          b) Relation between Degree Celsius and Degree Fahrenheit:

          ⁰C = ( ⁰F – 32) * 5/9

The temperature at which both degree Fahrenheit and degree Celsius values are same is -40.

          i.e. – 40⁰F = – 40⁰C

• We know that the matter can exist in the three states: Solid, Liquid and Gas. All these three states are interconvertible. We can change the state of a matter in three ways:

          a) By changing the temp.

          b) By changing the pressure

          c) By changing both temp. and pressure

• This temperature at which a liquid starts boiling and changes into the gas at atmospheric pressure is called boiling point of the liquid.
• The extra heat which does not raise the temp. of the substance is called the Latent heat. This latent heat, also called hidden heat is used to change the state of the substance.
• the heat required to change the unit mass of a solid to liquid without any change in temperature is called the Latent heat of fusion
• the heat required to change the unit mass of a  liquid to gas without any change in temperature is called Latent heat of vaporization:

CBSE Class 9th: Matter in Our Surroundings – Evaporation