Why do things change colour when heated
At some stage you would have seen a piece of metal change colour when heated. If you think you haven't look at a light bulb.
A light bulb contains a small strip of tungsten. When a current is sent through the metal, it heats up. This causes the tungsten to change colour from silver to bright white.
But how does this work?
First thing first, what is light and what is it made of?
Light is made up of small particles called photons. These photons oscillates along a wave length. The more they oscillates the more intense the wave length.
Gamma rays are the most intense form of light energy, while radio waves are the weakest form.
Now that we know what light is, why is it that objects look the colour that they are.
The reasons objects look the colour that they are is because they reflect that colour back into our eyes and absorb every other colour.
White light is made up of every colour in the visible light spectrum. Meaning is an object looks white, outside, it is reflecting every colour back into our eyes.
If it looks blue, it is absorbing every colour but blue.
Throughout the electromagnetic spectrum, there is a small portion called visible light spectrum.
At this stage the photons are oscillates at the right wave length to produce the colours we see. Each colour has its own wave length.
Another reason some objects may look a specific colour is because they emit a specific wave length.
The sun dose not reflect or absorb different forms of light, but emits all wavelengths which is why it looks white.
So getting back to why things change colour when they heat up.
We know that everything is made up of atoms, and when we heat these atoms they begin to vibrate. When they vibrate they emit electromagnetic waves.
Objects which emit a blue colour are generally hotter than objects emitting a red/yellow colour (look back at the electromagnetic spectrum).
For example a star which burns blue has a surface temperature of 60,000 K, while a red star has surface temperature of only 3,500 K.
On a side note it is important to know that temperature and colour are not always linked.
If we change what we burn, we can change the colour of the flame without changing heat.
- Strontium Chloride=RED
- Sodium Carbonate=YELLOW
- Cupric Sulfate=GREEN
- Potassium Chloride=PURPLE
- Cupric Chloride=BLUE
https://www.youtube.com/watch?v=2xDwIuUFjws
So why does metal change colour when its heated?
When we heat a piece of metal we are adding thermal energy to the atoms within the metal.
This causes them to start vibrating and then they begin to emit electromagnetic radiation.
When we start to heat a metal rod, you’ll notice it first glows red (lowest frequency). As we continue to heat it (giving more energy), it will eventually turn a bright white (all the visible spectrum).
This is because the atoms in the metal are vibrating so much that they emit a high electromagnetic frequency, which we see as different colours.
