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Old Sep 14th 2009, 11:32 AM   #1
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Question constancy of the speed of light or electromagnetic waves

According to SR speed of light is same for everyone.
But light is an example of electromagnetic waves, so we can say that speed of electromagnetic waves is same for everyone?
Is speed of all types of electromagnetic waves is same, like radio, infrared, microwaves etc?
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Old Sep 14th 2009, 10:08 PM   #2
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Yes all electromagnetic waves have the same speed whether radio, microwave or infrared. In fact when Maxwell found the velocity of electromagnetic waves from his equations, it was found that it matches the vel of light and that is when it was realized that light is also an electromagnetic wave.

What changes from one type of wave to the other is the frequency and consequently the wavelength also, but all travel at the same speed.

If it is difficult to understand how two such waves can travel at the same speed try the following visualization.

Think of two snakes a long one and a short one moving beside each other at the same speed. The short one will have to wiggle much faster (higher freq) to keep up because its "wavelength" is shorter.

Or think of a man walking with a small dog. The dog will have to take many steps quickly to keep up with say one step of the man.
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