Radiation

Radiation is a process of heat transfer which requires no intervening medium for the transfer of heat from one body to another.

Under this process, the heat can travel through vacuum.

Heat radiations are not themselves hot but when they are absorbed by an object the object becomes hot.

 

Activity L

Thermometer in the black colored beaker will record a greater rise in tempera- ture then the thermometer in the polished beaker.

Activity M

Keep hot water in two beakers and place them in a shade and record the temperature The water in the black colored beaker cools faster than that in the polished beaker.

Deductions

Black surface in good absorber and good radiator while polished surfaces are good reflectors but poor radiators of radiant heat.

The rays coming to us from the sun are often called as radiations.

 

Three types of Radiations :

Ultra –violet Radiations Visible Radiations Infra Red Radiations

Eyes can see only the visible radiation. They form light rays. Infra Red radiations in the Sun rays are the heat Radiations

Heat radiations always travel along straight line paths. Their speed of travel in vacuum is = 3 x108 m/s

Good absorbers of heat are good emitters of heat while poor absorbers of heat are poor emitters of heat.