The Physics of Light?

Question

Hello,
If light contains a certain (particle/wave) duality, then is it possible for photons to not have a constant velocity? In short, can light slow down in particular cases?

Answer 1

The velocity of light is NOT constant! It depends on the material through which the light is traveling and is given by the formula

c = 1/√[eµ]

where e = electrical permittivity and µ = magnetic permeability of the medium, both physical constants. This formula comes from the solution of Maxwell's equations. In fact, the ratio of velocity in vacuum to the light velocity in a medium is called the INDEX OF REFRACTION of that medium; the change in velocity on crossing the boundary between two media of different indices of refraction causes the light beam to bend (refract).

HOWEVER, the velocity of light (whatever value it has) is independent of the velocity of the observer and the velocity of the source.

In fact, physicists have been have to make light move very slowly; see http://en.wikipedia.org/wiki/Slow_light

Answer 2

Nope. Light travels at light speed. Now when light travels through an optically dense medium, it seems to slow down. But this has nothing to do with wave/particle duality. It's just that the stuff that is propagating through the medium isn't just light. It's a combination of light and charged particles. The charged particles travel slower, so the "light" goes slower than light.

But electromagnetic disturbances propagate at the speed of light. Period.

Edit: re answer below--you have studied refraction, right? When light travels through glass, the disturbance (which isn't exactly light) travels at less than light speed. So to be precise, we say that the APPARENT speed of light slows down. The speed of honest-to-God pure E-M radiation, however, is always c.

Answer 3

Einstein’s theory of special relativity is solely based on light traveling at a constant speed at all times and from all points of reference. He was smarter then me so I’ll agree with him. Light will never slow down.

The guy above is wrong, light never even "seems" to slow down. It has a constant speed no matter how it is viewed.

Answer 4

Light has a constant speed in a medium but different speeds in different media so yes you are correct, Light can travel slower as it travels from one medium to another. You can see this as light bends as it enters water. This is known as refraction.

Answer 5

Yes of course, speed of light depends on the medium in which it is traveling. The speed which we all know 3*10e8 is the speed of light in air(refractive index = 1). The speed in the medium depends upon the refractive index of the medium and hence be calculated easily.

Answer 6

Snell's regulation: n1 sin(theta1) = n2 sin(theta2) ascertain on your mind-set of incidence: theta1 = arcsine ( sin(theta2) n2 / n1) they offer you the mind-set of refraction, theta2. you're prepared to anticipate that air has an index of refraction n1 = a million. you truly may favor to seek for the index of refraction of water, n2. Then plugnchug. in basic terms to quibble with goulden--consistently do your fixing till now you do your plugging. you do now no longer favor to be doing algebra with numbers and gadgets already floating round.