Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: katieHaylor on 27/06/2017 08:59:30
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Yashwanth says:
When light is reflected off of a surface, what actually happens at the point of reflection? Is the light decelerating, stopping, and then reversing its direction, getting back up to its original speed?
What do you think?
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Is the light decelerating, stopping, and then reversing its direction, getting back up to its original speed?
Light is quite unlike material objects with which we are familiar.
In a vacuum, light always travels at the same speed = 299,792.458 km/second.
This speed is so important that physicists give it a name, "c".
In a vacuum, light (or any electromagnetic radiation) cannot travel slower than c, so it can't slow down, stop and then accelerate back to c.
To light, air is almost a vacuum; light travels a tiny bit slower than this in air. But it still can't slow down or accelerate in air.
In the described scenario, there is a small time when the light is interacting with the metal surface.
- You could imagine that the electric and magnetic fields of the light interact with the electrons that float freely through the metal. This sets up a current in the metal surface that has characteristics equal and opposite to the incoming light (in fact, you could say that it is a "mirror image"). This electromagnetic field cancels the original light wave, and produces another heading out of the metal, in a direction that follows the rule "the angle of incidence equals the angle of reflection".
If it is a glass-covered mirror, there is a small period when the light passes through the glass.
- For the small amount of time that the light is passing through the glass, it travels at about 2/3 of c, or around 200,000 km/second.
See: https://en.wikipedia.org/wiki/Reflection_(physics)#Reflection_of_light
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We are limited by our inertia to speeds much slower than the speed of light. This makes it hard to appreciate what is going on. Uncertainties in measurement only exacerbate the situation. To really understand what happens would require apparatus that is well outside our capabilities to imagine or construct.