3. Radiation

Radiation is the continual emission of infared waves from the surface of all bodies, transmitted without the aid of a medium.

Radiation..
-unlike conduction and convection, it does not require a medium for energy transfer.
-can take place in a vacuum (without any matter)

For radiation, heat is transferred by infra red waves.

eg.
-The heat from the Sun is tranferred by radiation to the Earth.
-This is something conduction and convection cannot do as there is no medium between the Sun and the Earth.
-Another example will be campfire.
-We could feel the heat from the campfire even though there is no medium in between.

Emission of infared radiation
All objects and surfaces emits infared radiation and this emission causes the temperature of the objects themselves to fall.

What are the factors affecting the rate of heat tranfer by radiation (infared radiation)? [both emission and absorbsion]

1. The colour and texture of the surface of the body

Black or dull suraface
- best radiator of heat, better absorer of infared radiation.
- better emitter of infared radiation

Shiny or white smooth surface
- worst radiator of heat, worse absorber of infared radiation.

2. The surface temperature of the body
The higher the temperature of the surface, the higher the rate of radiation.

3. The surface area of the body
The larger the surface area, the higher the rate of radiation.

Other facts on radiation...

-If the temperature of the object is higher than the surrounding, it
is a net emitter of radiation.
-If the temperature of the object is lower than the surrounding, it
is a net absorber of radiation.

-A rough and dull black surface is both a good emitter and a good absorber.
-A smooth and polished surface is both a poor emitter and a poor absorber.

Infared radiation cannot be seen with our naked eyes but the heat sensitive camera can shot the hot spots.

eg.
The hottest spot of the cat is its nose as seen by the camera.


A video by 'Eureka' on the topic, radiation waves.