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COLOUR OF TEMPERATURE

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          Why the gas stove gives out blue flame?  Let us explore.

     Origin of light:
     When the charges (electrons, ions) vibrates, oscillating electric field is created.  Oscillating electric field subsequently gives rise to oscillating magnetic field.  Now the electromagnetic wave is born.  It will start to spread out. If the wave's frequency falls within the visible range, it is light.

     Invisible Infra-red:
     All the bodies in this world or in this universe have some temperature above absolute zero kelvin.  Hence, atomic particles[charges] in these bodies execute vibrations due to heat.  They will start emitting electromagnetic waves[light waves]. If their temperature is less than 1000 k,  the frequency of waves will fall in infra-red range.  Humans, animals, trees, houses ...   always emit IR radiations.  Hence they can be detected even in night using infra-red cameras and Binoculars.

Red Hot:

     If we heat steel piece, it will glow with red light.  Its temperature must be around 1000 k.  They emit visible radiations in the frequency of red light.

Yellowish -sun:

     The surface temperature of the sun is 5000 k.  It emits whitish -yellow light.  White light indicates that the radiations is emitted in all seven colours.  Yellow  may dominate them.  The Tungsten filament in a bulb also burns in this temperature.

Blue flame:

     When the temperature reaches around 10000 k, pure blue light is emitted.  Bunsen burner, cooking gas stove emits blue flame.  Since blue indicates high temperature, blue flame is always desired for cooking, heating, welding purposes.

Violet and ultra-violet:
     When the temperature goes beyond 10000 kelvin, violet and ultraviolet is emitted.  UV light, indicates high temperature, hence it is used to kill germs.

A thermal kaleidoscope:

     In an iron-smith workshop, a piece of iron is heated in a furnace.  From cold black, it turns to red, orange yellow, white and whitish blue as the temperature rises.  It is called "incandescence " and it is said to emit continuous spectrum.

Warm and cool colours:
     In literature, yellow and red are said to be Hot and violent colours.  Blue and violet are cool ones. In science, it is exactly opposite as explained above.  We can also illustrate this with example.  In the early morning, the sun is reddish and cool; late morning, it becomes yellow;  In mid-day, it yields clear blue sky; as the temperatures progresses.

Note:
     What we have seen is the basis of black body radiation.  It turned physics upside-down and gave birth to quantum physics.   
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