Radiation of Heat and its Applications

All of us have experienced the pleasant heat from the sun in the winters . . .

. . . as well as it's scorching heat in the summers.

But how does this heat of the Sun reach us even from millions of kilometers away?

The answer is . . . RADIATION

is the process of heat transfer in which heat directly passes from one body at higher temperature to another body at lower temperature without affecting the medium.

Note : heat transfer by .

That's why heat can pass from the sun to the earth easily though there is only vacuum in between.

The other two ways of heat transfer, i.e. and don't work in vacuum because they need a material .

Let us see a simple example of heat transfer by Radiation.

We feel warm while sitting near a fire.

We don't get this heat by conduction because air is a bad conductor of heat.

We don't get this heat by convection either because hot air rises up. It does not move sideways or downwards.

So that means we must be getting this heat only by the process of .

How do Radiations interact with different objects in our surroundings ?

We have noticed that a black asphalt road becomes so hot in the daytime that it is almost impossible to walk on it barefoot.

On the other hand, there is no problem in touching the white clothes drying under the same sunlight. They are only slightly warm.

Any object becomes warm because of the radiations it absorbs. But why the degree of hotness is different in different objects?

Black and dull objects (like, an asphalt road) radiations and radiations. So they become more warm.

Whereas, white and shiny objects (like, white clothes) radiations and . So they are less warm.

To utilize this phenomena, the bottom part of a cooking utensil is painted black.

The black surface absorbs more heat radiations. So the contents in the cooking utensil get cooked rapidly.

On the other hand, in a room heater, we want more heat to be and not absorbed; and hence its surface is made .

Radiations also influence our choice of clothes we wear

In summers, we wish to keep our bodies cool. So we prefer white or light coloured clothes to reflect most of the sun's heat.

But in winters, we wish to keep our bodies warm. So we wear black and dark coloured clothes to absorb most of the sun's heat.

How is Radiation different from Conduction and Convection ?

Medium is necessary. Medium is necessary. Medium is not required.

In particles of medium do not leave their positions but they transfer the heat from one particle to the other by vibration.

In particles of medium leave their mean positions and move towards the colder region carrying the heat from the source.

In the medium in between remains unaffected.

Heat transfer can be in any direction. Heat transfer is only vertically upwards. Heat transfer is in all directions along straight paths.

The process is slow. The process is faster than conduction. The process takes place with the speed of light, i.e. So it is the fastest.

That's all for now! Let's have a small REVISION..

is the process of heat transfer in which heat directly passes from one body at higher temperature to another body at lower temperature without affecting the medium.

Black and dull objects absorb more radiations and reflect less radiations. So they become more warm with heat radiations.

White and shiny objects absorb less radiations and reflect more. So they become less warm with heat radiation.

Keep Learning. Keep Exploring :)