Why does light refract toward the normal

[physdoc]

why does light refract toward the normal when passing through glass?

 

[robphy]

It depends on the ratio of the indices-of-refraction.
http://en.wikipedia.org/wiki/Snell's_law

Here's a neat simulation:
https://phet.colorado.edu/en/simulation/bending-light

 

[physdoc]

It depends on the ratio of the indices-of-refraction.
http://en.wikipedia.org/wiki/Snell's_law

Here's a neat simulation:
https://phet.colorado.edu/en/simulation/bending-light

Do you mean to say that sometimes the light would not be refracted toward the normal, and sometimes it would, depending on the indices of refraction?

 

[robphy]

The paths of light are reversible.
Instead sending light from medium 1 to medium 2, send light from medium 2 to medium 1.
(Try the PhET simulation.)

Since the Law of Refraction says:
$n_1\sin\theta_1 =n_2\sin\theta_2$,
or equivalently $\frac{n1}{n2}=\frac{\sin\theta_2}{\sin\theta_1}$,
if $\frac{n1}{n2}<1$ (when entering a higher-n-medium),
then $\frac{\sin\theta_2}{\sin\theta_1}<1$... but this means $\frac{\theta_2}{\theta_1}<1$ since the sine function is always increasing between 0 and 90.

 

[physdoc]

Explain further

 

[physdoc]

The light slows down, but how can it be explained that this slowing down causes it to be refracted toward the normal?

 

[physdoc]

The light slows down, but how can it be explained that this slowing down causes it to be refracted toward the normal?

I answered it: because it covers less distance in the same time.

 

[robphy]

I answered it: because it covers less distance in the same time.

Yes... check out the "wave" (as opposed to the "ray") version of the PhET simulation.

 

[physdoc]

Thanks

 

[physdoc]

If you draw a triangle, with each of the rays as legs and connect them with a straight line running perpendicular to the normal, which shows that the original leg is longer than the refracted ray, right?

 

[Drakkith]

Remember that rays are only an approximation to real light, which is a wave. The light refracts towards the normal upon entering a medium with a higher refractive index because it travels slower inside the medium. See the image below. (Blue and Green arrows are the light ray)

Notice how the wavelength of the incoming light wave (blue lines) is larger than the wave inside the medium (green lines). This is because the speed of the wave is slower inside the medium than outside, while the frequency remains the same. The part of the wavefront first entering the medium is slowed down, allowing the parts yet to enter the medium to 'catch up' to it. When these later parts enter the medium they interfere with the part already there, and the interference of the different parts of the wavefront results in a change in the direction of the wavefront towards normal.