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Physics/Please clarify by doubts about the concept of Light and Photon


Do light or the photon particles travelling at the speed of light ever slow down or stop completely? What happens to light or the photon particles at that time?
In a closed chamber of reflective material, if light is emitted from a source for considerable duration, thereby emitting huge quantity of photons or so much light; and then the light source is shut off; what happens to the reflecting light or photon particles? Do they keep on travelling i.e. does the chamber keep lighted? If we wait for sometime after switching off the light source and create an opening, can we see light inside the enclosure or coming out from it?

Hello Monojit,

Light never stops moving - not if it is still something you could call light. Light can be absorbed by an object it hits. It then has contributed all its energy as heat to the object. All light (and all electromagnetic radiation - like radio signals) is one speed in a vacuum. It goes slower in other mediums. Air slows it down only slightly. Mediums that slow light down refract (bend) a light beam. That is how optical glasses correct vision problems for me and many other people.

Energy is lost each time light reflects off a reflective surface. Light travels so fast that many reflections would occur in a very short time consuming all light. So short a time that if you were in the chamber, you would not notice a gradual loss of light, it would seem to be immediate.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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