1st Nov '25

Radiation

All hot objects emit ( out) electromagnetic radiation. For most objects, at common temperatures, the radiation is limited to the part of the spectrum. As the object is heated the frequency of the radiation to the point at which it becomes visible to the human . At this point the object is said to be red hot. If it is heated further then it emits green light mixing with the red light to form orange. Still further and then light is emitted, mixing to produce light. The hottest stars in the sky in fact glow hot.

As with all electromagnetic waves, the radiation does not require a medium to travel through and so can cross a vacuum, just as the heat from the reaches us through space. When standing in the sunshine you feel the sun's heat more if you are wearing . This is because dark, matt surfaces absorb more radiation than , ones - these tend to reflect it instead.

For objects at the same temperature, , objects will emit more radiation than , ones. We say that black objects are both good emitters and absorbers of radiation.

If we have a hot object we want to stay warm, we should paint the surface of the container .
If we have a hot object we want to cool down, we should paint the surface of the container .
If we have a cool object we want to heat up, we should paint the surface of the container .
If we have a cool object we want to stay cool, we should paint the surface of the container .