Why Is the Angle of Incidence Crucial in Understanding Light Refraction?

[peter.ell]

I am a very conceptual kind of person and I'm trying to understand refraction, but after all my reading I'm still having some fundamental gaps that are preventing me from fully grasping it.

(All of these questions are especially pertaining to how light waves refract.)

Here's what I don't get:

1.) Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media. But what does it really mean to say that the sines of the angles of incidence are equivalent rather than the angles themselves as in the law of reflection?

2.) What is so important about the angle that a wave makes with the normal? If refraction is physically due to the wave's speed being slowed and it's wavelength shifting accordingly, then why is the degree of bending so dependent on the angle it makes with the normal? A light wave striking a piece of glass perpendicular to its surface, for example, will not be bent, it will go straight through, while a light wave striking that same piece of glass at an angle will not pass right through but will be bent first. What physically explains this, other than Snell's Law which just states it?

3.) Is there any physical explanation as to what causes a wave to bend toward or away from the normal depending on how its speed is changing?

Thank you so much for the help!

 

[JeffKoch]

Snell's law can be derived in various ways, you might start with that - the Wiki article on the topic has some useful graphs and animation, but it's more instructive to derive it and then refine any questions. Note that reflection and refraction are not different.

 

[Dr_Morbius]

If you think of the wave front as being like a line then as the bottom of the wave front hits the refracting material it begins to slow down while the top is still moving at its original velocity this causes the wave front to seem to rotate down towards the refracting surface.

http://en.wikipedia.org/wiki/Refraction

 

[sophiecentaur]

The wavelength in each medium is proportional to the speed. At the interface, the peaks of waves on each side must coincide as the wave passes through (a necessary boundary condition). This means that the angle must change to accommodate these two requirements. The geometry leads to Snell's Law. This is a bit of book-work that makes sense and is pretty understandable by anyone who can handle simple geometry.

 

[sardar]

I understand that concepts like refraction can be difficult to fully grasp. It takes time and effort to understand the underlying principles and mechanisms behind a phenomenon. I will do my best to address your questions and help you gain a better understanding of refraction.

1) Snell's law is a mathematical relationship that describes how light waves behave when they pass through different mediums. The ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of the phase velocities in the two media. This means that the change in direction of the light wave is directly proportional to the change in speed as it passes through the different medium. In contrast, the law of reflection states that the angle of incidence is equal to the angle of reflection, which is a simpler concept to understand. However, in refraction, the angle of incidence and refraction are not equal because the speed of the light wave changes as it passes through the medium. This is why Snell's law uses the ratio of the sines instead of the angles themselves.

2) The angle that a light wave makes with the normal is important because it determines the amount of bending that will occur when the light wave enters a different medium. This is because the speed of the light wave changes as it passes through the medium, and the degree of bending is dependent on this change in speed. When a light wave enters a medium at a perpendicular angle, there is no change in speed and therefore no bending. However, when the light wave enters at an angle, the change in speed causes the light wave to bend. This can be explained by the wave nature of light, where the wavelength changes as the speed changes, causing the light to bend towards or away from the normal.

3) The change in speed of the light wave is caused by the change in the medium's refractive index. The refractive index is a measure of how much a medium slows down the speed of light. When a light wave passes from a medium with a lower refractive index to a medium with a higher refractive index, it will slow down and bend towards the normal. On the other hand, if it passes from a medium with a higher refractive index to a medium with a lower refractive index, it will speed up and bend away from the normal. This change in speed is what causes the bending of the light wave.

I hope this helps to clarify your understanding of refraction. Remember that it is a complex phenomenon