The radiation and the heat- Why light cause heat

Heat and radiation related very much with each other, a hot body must release radiation and a radiation must cause heat. Heat is that energy which get converted into kinetic energy from EM radiation. Well, how kinetic energy? When radiation falls onto the surface of any body then it starts transferring their energy to the molecules of that body and due which their molecules starts vibrating. And that vibration of the molecules, we call it heat. We all know, heat get transferred by two means, the first is when a body touches another body and second mean is the radiation. In this whole article I am talking about electromagnetic radiation. So whenever I call radiation then I am calling electromagnetic radiation. If two body comes in contact with surface to surface and if there is some temperature difference between them, then the heat starts flowing from hotter body to the cooler body. And when their temperature becomes equal to each other then it stops flowing or now entire molecules have the same kinetic energy. 

When light (radiation) strikes a body (atom), it transmits energy to the electron of its outer most shell due to which the electron jumps to the higher energy shell and instantly returns to its original place. This jumping process gives some kinetic energy to the molecule. And rest of them release as light (radiation) having longer wavelength than the incident light. 

Different body have different property to absorb light some of them get warm easily and some do not. Bodies which has darker colour absorb light more than a lighter one or most of the light which falls on to it get converted into longer wavelength (I.e the radiation which has less energy). As we know, radiation having higher frequency (shorter wavelength) have higher energy than the radiation having lower frequency (larger wavelength). For example-X- ray is more power full than UV ray, as it has higher frequency than UV. But don't take this sense for ionization. 

So, when light falls on a darker body then it's most of the energy get converted into heat and rest of them release out as light having less energy. So, darker body absorbs much light than lighter body and get warm easily than a lighter body. This phenomenon is same for lighter body but in this case most of the light get released and very few of them get converted into heat.

Why hotter body release IR radiation?

As I have described that when a body is hot, it's molecules have some kinetic energy. And due to this kinetic energy it's molecules strikes each other and due to which some amount of light energy get released. A hot body not releases only infrared radiation, it can release the radiation of almost all frequency. Light energy which can released by an hot object is totally dependent on its temperature. Higher the temperature, higher the frequency. You can observe it at a black smith shop as I had observed. When the smith put a iron rod in the furnace then the temperature of that rod start increasing, for the first few minutes you can't see any glowing in the iron rod, at that time it is releasing infrared radiation, but with time you can see some glowing in the iron rod. The temperature of the furnace is not too much that's why you can only see red light but if you can put this rod in to the center of the sun then you can see even x- ray or gamma ray,  oh! I'm sorry, you can't see x-ray or gamma ray.

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