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I am a 10th grade student.I have seen that when a metal is heated it's color changes.But I cannot understand how heating a metal changes it's color.

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By heating metal you are providing sufficient energy for the excitation of electron from specific orbital to another high energy orbital but after a very small and i meant a very small period of time the electron de-excites to lower energy orbital releasing energy of specific wavelength. So by changing or varying temperature and providing heat to metal the electron continuously excites and dexcites providing different wavelength of light.

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  • $\begingroup$ I feel the thermal radiation intensity can not be coupled to electronic transitions as the radiation available is continuous at any temperature T,whereas the electronic transitions will lead to bands of particular emission lines. $\endgroup$ – drvrm Apr 15 '16 at 17:49
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If you're meaning the tempering colors (that rainbow look after heating), that would be a very thin layer of oxidation. The more metal heats up, the easier and deeper it oxidizes. Each level of heat creates a different depth of oxidation that will reflect a specific wavelength of light and absorb all other wavelengths. The colors you see represent the different colors being reflected based on how deep the oxidation which is based on how hot the metal got at that area. That's why it shows up in bands of color. The dark blue is closest to the heat source and so hotter. The "straw color" is further from the heat source and so only barely got hot enough to begin tempering to a color. Metal workers can use these colors to help them know when a steell is a specific color so they can temper it for hardening and toughening processes.

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Radiation what we see as color is due to the emission of light waves (electromagnetic) from all material that has a temperature representing its state of internal energy.

The glow we see is the conversion of its internal energy into radiation. At any temperature the kinetic energy of movements of atoms and molecules in matter leads to thermal energy.

We know that in a material atoms/molecules are arranged in a particular fashion and normally bounded by their atomic bonds.

These atoms and molecules are composed of charged particles for example electrons and protons , and interactions among matter particles result in acceleration of charges and oscillations of charge dipoles.

The above motion can emit electromagnetic radiation.

One can say that all matter at a temperature(T) by definition is composed of particles which have kinetic energy, and which interact with each other. This results in the electro dynamic generation of coupled electric and magnetic fields, resulting in the emission of photons (the particle representing light radiation), radiating energy away from the body through its surface .

As the temperature of the body increases the frequency of emitted radiation also increases thats why one sees a variety of colors as the body gets raised to higher temperature.

Some popular colors and their temp of the body is listed below

T(degree centigrade) ; Emission color

580 °C              dark red
730 °C              bright red(slightly orange)
930 °C              bright orange
1,100 °C            pale yellowish orange
1,300 °C            yellowish white

Reference >:https://en.wikipedia.org/wiki/Thermal_radiation#Subjective_color_to_the_eye_of_a_black_body_thermal_radiator)

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