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Radiation

Heat transfer by radiation

Heat can be transferred by infrared radiation. Unlike conduction and convection, which need 

particles, infrared radiation is a type of electromagnetic radiation that involves waves.

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Radiation can even work through the vacuum of space. 

This is why we can still feel the heat of 

the Sun even though it is 150 million km away from the Earth.




Light from the sun reaching earth


Different surfaces

Some surfaces are better than others at reflecting and absorbing infrared radiation. The table summarizes some differences.

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Differences in surfaces absorbing radiation 
 Surface  Ability to reflect infrared radiation Ability to absorb infrared radiation 

 Dull or 
rough


 Poor
 
 Good
 
Shiny


 Good

 Poor

If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object. This is one reason why domestic radiators are thin and flat. Radiators are often painted with white gloss paint. They would be better at radiating heat if they were painted with black matt paint, but in fact, despite their name, radiators transfer heat to the room first by radiation then most of the heat transfer to a room by convection.



  Application on radiation



Cooling fins that is placed at the refrigerator

The cooling fins at the back of refrigerators are also painted black. However, these are used to radiate heat quickly to the surroundings.

If this fins are made of shiny surface it will reflect the infrared inside the fins  therefore Freon gas inside it will always be hot. and this is dangerous.














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