Please explain refraction at the atomic level.?

Question

We see refraction with marbles rolling on a plane encountering either a ramp up or down. It is another force, gravity that causes the refraction of the marble. What is the other force that is applied to the photon that causes it to change direction when entering glass say?
The angle of refraction infers that the photon is speeded up, and yet the texts refer to photons being slowed by their passage through glass. Also, what the heck is going on with double-refraction? Are the two beams travelling at different speeds through the same media?

Answer 1

You don't need QM to explain refraction. You need to know about waves, though.

Light waves travel at different speeds in different media. Imagine you are looking down at a beach and a train of waves marching (at an angle) toward the beach. The parts of the wave front closer to the beach travel more slowly, and so the wave front seems to bend toward the beach. Also notice that the waves sort of "pile up". As they travel more slowly, but more waves keep regularly arriving, the inter-crest spacing (the wavelength) decreases. This makes sense, since speed=wavelength*frequency, and the frequency remains the same, so the only way to slow the wave is to decrease the wavelength.

Bacl in the day, there was quite a bit of controversy over the mechanism of refraction. Some believed that, just as in your class demonstration, the light accelerated in the direction of the normal between the media. This is the oppopsite of te beach effect--it would tend to increase the wavelength. Others believed the beach model.

The controversy was resolved in favor of the wave theory, and light actually does travel more slowly in materials than it does in vacuum.

To understand the reason why the light slows down, a simple classical model actually suffices. Light jiggles the electrons within the atoms, and (according to the classical theory as well as the quantum) accelerated charge will radiate more light. The light wave in the material is the combination of all the light--the original as well as the interactively created, and if you are carreful about all the contributions, you end up with the right wavelength.

As for double refraction, recall that light has a polarization: the electric field vector points perpendicularly to the direction of wave propagation. Some materials respond differently to electric fields in different directions: the electrons jiggle more or less depending on which way you try to push them. Therefore the speed of the wave changes depending on which way the electric field points. You can split the electric field of the incident wave into components corresponding to the different directions, and so for an incident wave in general you'll have different angles of refraction, one for each polarization.

Answer 2

both mirrored image and refraction are a really effective source of the identity of a mineral species .(mild) both one among it is the attitude of making use of mild to the floor of a gem . mirrored image at the same time as utilized to the crown of a gem will leap off the alternative route on the attitude it is strictly equivalent to the attitude in which it hit the stone . Now Refraction at the same time as utilized to the floor of a gem, enters into the gem at an oblique route. particularly of vacationing instantly with the aid of the gem its direction turns into altered , hence bending the ray is refraction . The length of the attitude of the mild it reflects is mild refraction.. contained in the attitude of this try a significant identity of any gem species at the same time as it is checked adversarial to the table of Refractive Ind ices. each and every gem has its own refractive index .

Answer 3

I'm sorry I don't have a concise answer, but I know you may be trying to think about it in terms of classical physics.

When you get into the quantum effects, this is explained much better. The idea is that it is just the angle that is most probable and that's what we see on average.

Feynman's book is great for this in laymen's terms.