Other Concepts Importent Definitions Chapter 1 Science Class 9 Notes Chapter 1 Matter in Our Surrounding Science Class

Melting Point: The temperature at which the solid starts melting to become a liquid at the atmospheric pressure is called its melting point.
Boiling Point:  The temperature at which the liquid starts boiling at the atmospheric pressure is called its boiling point.
Latent heat of fusion: The amount of heat energy required to change 1 kg of solid into liquid at atmospheric pressure at its melting point is called the latent heat of fusion.
Latent heat of vaporisation: The amount of heat energy required to change 1 kg of liquid into gas at atmospheric pressure at its boiling point is called the latent heat of vaporisation.
Sublimation: There are some substances that change directly from solid state to gaseous state and vice versa without changing into liquid state. Such substances are called sublime and this process in known as sublimation.
Why do we see water droplets on the outer surface of the glass containing ice-cold water?
Sometimes we see water droplets on the outer surface of the glass containing ice-cold water this is because the water vapour presents in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

 What is Dry Ice?
We know that gases can be liquefied by applying pressure and reducing temperature. When carbon dioxide is stored under very high pressure it becomes solid and known as solid CO2. Solid CO2 gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.