Radiation

Define Radiation:
The transfer of heat energy from a hot body to a cold body directly without heating the space in between the two bodies is called radiation

Example:

 When we sit in the sun or infront of a heater , we feel warm heat energy reaches us by radiation, radiation is the only type of heat transfer by which the suns energy can move to the earth because heat can not reach to earth by conduction or convection.

Good and bad radiators and absorbers of heat...?

Black surfaces are good absorbers and good radiators of heat  while shiny surfaces are bad absorbers and bad radiators of heat.

Example:

shiny teapots and utensils can keep food or tea warm for a longer time then black ones. 

shiny containers can also keep cold liquids cool for a longer time then black containers

Application of radiation of heat:

1. When we sit beside a fire , the heat of fire reaches us by radiation.

2.The black cooling fins at the back of refrigerator radiate heat quickly.

3.During hot summer days , it is advised to wear white or light coloured clothes. white colour absorbs less heat than dark colours

4.Radiation from the sun passes through the glass or plastic of green house and wars up the soil and plants . plants and soil absorb and emit radiation and increase the temperature in the green house due to which plants grow well