# Talk:Refraction

WikiProject Physics (Rated B-class, High-importance)
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
B  This article has been rated as B-Class on the project's quality scale.
High  This article has been rated as High-importance on the project's importance scale.

This seems lacking. Where're the history and mechanism? lysdexia 13:49, 27 Oct 2004 (UTC)

## Category

Physics. You need to put this in physics also because earthquake waves or seismic waves follow the same pattern using refraction. when an earthquake wave - either a P or S wave - travels through the earth, the mantel it flows through changes density as it gets closer to the epicenter the core because of gravity. The core it self has 2 layers - a liquid outer and a solid inner. Only P waves can travel through the core because they can travel through both liquids and soilds (mantel is solid - its a type of rock). Why this has anything to do with refraction is because as the waves move throught the earth is follows a curved path. why? because the change in densitys from gravity change the course of the wave. This is why the earthquake waves do just go straight through the earth from england to australia, instead an earthquake will be made everywhere in the earth but losing it 'shake' as it travels further along the earth. —Preceding unsigned comment added by 81.174.154.192 (talk) 14:33, 26 February 2011 (UTC)

Well I've put it in optics. it might need to go in other categories too though. Theresa Knott (Tart, knees hot) 21:51, 14 Nov 2004 (UTC)

## Image Changes

Hi, this article looked weird on a wide monitor (1920 pixels). The "See Also" section appeared to the right of the eye image, and the whole thing looked cluttered and confusing.. It wasn't clear what image the "In this diagram..." text referred to. On Safari or Firefox, it looked completely broken; the "In this diagram..." text overlapped the eye image. So, I moved the "In this diagram..." text to the image caption, and moved the image to the right. I removed the ripple tank image because it didn't seem that helpful, and there are too many images for the amount of text. Before reverting anything, please look at the old page on a wide monitor on safari or firefox... Pfalstad 8 July 2005 03:41 (UTC)

you need to put this in physics also because earthquake waves or seismic waves follow the same pattern using refraction. when an earthquake wave - either a P or S wave - travels through the earth, the mantel it flows through changes density as it gets closer to the epicenter the core because of gravity. The core it self has 2 layers - a liquid outer and a solid inner. Only P waves can travel through the core because they can travel through both liquids and soilds (mantel is solid - its a type of rock). Why this has anything to do with refraction is because as the waves move throught the earth is follows a curved path. why? because the change in densitys from gravity change the course of the wave. This is why the earthquake waves do just go straight through the earth from england to australia, instead an earthquake will be made everywhere in the earth but losing it 'shake' as it travels further along the earth. —Preceding unsigned comment added by 81.174.154.192 (talk) 14:30, 26 February 2011 (UTC)

## improvement

I think this article needs more technical content. 203.98.102.12 19:22, 13 January 2006 (UTC)

the image provided also shows the aparent image rotated upwards from the object. this is incorect as it should be directly above the object. (ie rotated upwards and shortend). plz excuse spelling =) —Preceding unsigned comment added by 219.89.95.106 (talk) 08:28, 26 June 2008 (UTC)

I think that index for air should indicate the air pressure (e.g., one atmosphere) and the absolute humidity. I haven't checked it out but I would suppose that the provided index for air is at one atmosphere and zero percent humidity. Also, maybe some mention should be given that refraction tends to follow material density. I believe that there are a couple weird (i.e., laboratory) examples where refraction values didn't follow density. (But I could be wrong.) - WayneH 20:46, 19 August 2008 (UTC)

I'd love to see a derivation from maxwells equations and surface boundary conditions —Preceding unsigned comment added by 217.72.84.137 (talk) 19:18, 20 March 2009 (UTC)

how can the wavelength increase or decrease, yet the frequency remain the same, given that frequency has an inverse relationship to wavelength?

The wave's velocity is altered at the boundary between the two media. velocity of wave = frequency * wavelength. Frequency remains the same, but wavelength and velocity are both different in the two media. Pfalstad 17:27, 23 October 2006 (UTC)
Indeed, the wavelength has to change, because light travels slower in a medium than it does in vacuum (or a sparse medium like air). One can imagine the wavefronts "bunching up" as they move into the medium where light propagates slower—the wavelength becomes shorter in the denser medium.--Srleffler 22:30, 23 October 2006 (UTC)

"The waves (water waves) travel more slowly in the shallower water." Why?

## Incorrect definition

According to the article

"Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another."

The causal relationship stated is incorrect. The change in velocity (direction AND speed) is caused by passing from one medium to another. Also, by definition, refraction is the change in the direction of a wave passing from one medium to another with a different refractive index. So this is incorrect:

"This is most commonly seen when a wave passes from one medium to another." —Preceding unsigned comment added by 119.94.125.10 (talk) 15:17, 17 September 2008 (UTC)

I have only one question, why? There isn't a sensible explaination to the phenomena of refraction here. I remember vaguely there was a quantum mechanic explaination for this in the article some years back. —Preceding unsigned comment added by 218.186.12.204 (talk) 14:12, 1 February 2009 (UTC) I have added "easier explanation". It might help. 84.16.123.194 (talk) 12:45, 18 May 2009 (UTC) Consider the "first atom" concept related to the refraction of a beam of light. It is evident that there has to be an immediate stress/strain relationship in the reaction of the atom to the stress of the passage of the light wave/energy material. It would also have to be the sum of the stress over an integrated time interval. But since all the different light wave frequencies arrive with the same speed of propagation, it is doubtful that the speed of the passing of the wave/particle material is the guiding factor resulting the angular deflection of the beam.WFPM (talk) 17:34, 31 August 2010 (UTC)

## Incorrect use of the term Velocity in the first line

The first line says:

"Refraction is the change in direction of a wave due to a change in its velocity."

BUT velocity is a vector quantity, meaning it has a magnitude and a direction. Therefore, the use of velocity is incorrect. To my understanding the sentence should either:

1. "Refraction is the change in direction of a wave due to a change in its speed."

or

2. "Refraction is the change in direction component of a wave's velocity due to a change in its speed component." (or words to that effect, as that is poorly worded).

may be wrong just though I'd point it out.—The preceding unsigned comment was added by Annannienann (talkcontribs) 14:00, November 6, 2006.

It's not outright wrong, but isn't good wording.--Srleffler 20:08, 6 November 2006 (UTC)
But different color frequencies of light waves arrive at a point of refraction at the same speed, and are nevertheless refracted by different amounts, So the light's frequency has to be a significant factor.WFPM (talk) 23:36, 1 September 2010 (UTC)

## Shouldn't wave refraction in the sea (water waves) get a look in?

we have nothing on the refraction of water waves. When I work out what it is, i'll write up on it (included in this article or seperate?)TDN 22:26, 23 November 2006 (UTC)

It's already in there. There is a paragraph on it, and two pictures.--Srleffler 05:46, 24 November 2006 (UTC)

Is it? I'll have a lookTDN 12:09, 10 December 2006 (UTC) Oh, it is. I wasn't looking carefully enough, but anyway, should there be a separate article about it? It is a different subject, coastal erosion, headlands, bays, beaches, etc. TDN 12:13, 10 December 2006 (UTC)

I'm not sure that wave refraction in water waves needs its own article. Look around carefully, you may find that there is already a lot of information on the behavior of water waves. Check out Ocean surface wave, Surface wave, and Gravity wave for various approaches to the subject. Coastal erosion may also be of interest.--Srleffler 20:08, 10 December 2006 (UTC)

## Way too many vague images

At the moment, the images actually make the article appear more sporadic -- there's no real need to have the whole gamete of refraction if there's not that much expansive information. Also, the soda straw thing DOES demonstrate refraction, but it's definately a more finite example of virtual imagery. James S 19:50, 12 December 2006 (UTC)

## Change in the speed of light

I got really puzzled trying to understand how could the speed of light be altered while reading this article, as I had long thought of it as the only universal measure. And took an hour thinking and searching to get the answer. Maybe linking this topic http://en.wikipedia.org/wiki/Speed_of_light#Interaction_with_transparent_materials somewhere could make it easier for people to understand it.

edit: Also, pure light would never undergo refraction or alteration of its speed? Sorry for not signing and editing this maybe not the way I should, I'm used to only reading wikipedia. thanks.

—The preceding unsigned comment was added by Japaa (talkcontribs) 23:09, 10 February 2007 (UTC).

"Pure light"? Photons, as opposed to electromagnetic waves?

The universal-measure part is only light in a total vacuum--I don't have a definite reason why light slows down in a medium (since it doesn't seem to lose energy), but...yeah. 24.16.140.208 (talk) 04:44, 15 February 2008 (UTC)

If you're going to believe that light slows down when passing through denser media, shouldn't you then have an explanation of how it manages to speed back up after it exits the media.WFPM —Preceding unsigned comment added by WFPM (talkcontribs) 11:16, 28 August 2009 (UTC) Oh yes, now I see it in the Dispersion section about the Speed of light.WFPM (talk) 11:35, 28 August 2009 (UTC)

I can't find an explanation of why it slows down (I might be missing it). Is it related to the presence of atoms and the influence of mass (gravity) on the passage of time?Ninahexan (talk) 04:10, 9 February 2011 (UTC)

It is true that it is not light that slows down. It is the interactions within the medium that slows it down. At least a partial explanation, contained within this article is here. I think I use to have access to a more complete explanation, but the speed of light article appears to be different in some parts (since the last time I looked). So, I recommend reading that article - it should be in there somewhere.
"At the microscale, an electromagnetic wave's phase speed is slowed in a material because the electric field creates a disturbance in the charges of each atom (primarily the electrons) proportional to the permittivity of the medium. The charges will, in general, oscillate slightly out of phase with respect to the driving electric field. The charges thus radiate their own electromagnetic wave that is at the same frequency but with a phase delay. The macroscopic sum of all such contributions in the material is a wave with the same frequency but shorter wavelength than the original, leading to a slowing of the wave's phase speed. Most of the radiation from oscillating material charges will modify the incoming wave, changing its velocity. However, some net energy will be radiated in other directions (see scattering)."
Well, good luck. ---- Steve Quinn (talk) 07:04, 9 February 2011 (UTC)
Also, I am talking about ordinary materials - not cold atoms and lasers. ------- Steve Quinn (talk) 07:26, 9 February 2011 (UTC)
Visting the above italisiczed explanation once again, I see that this gives a good explanation of why light slows down in a material. I think I misunderstood the question (or something) (or I was tired?). ---- Steve Quinn (talk) 07:21, 1 March 2011 (UTC)

I think this article misses the important point of why the speed of light is lower in a medium, its direction changes, or, how light travels in a medium. —Preceding unsigned comment added by 84.120.147.185 (talk) 07:56, 23 May 2011 (UTC)

## Only when it hits the boundary at an angle

Assuming that refraction is only observed when the wave changes direction (rays change velocity) why does it not mention that it is only observed when it reaches a boundary (at which a speed change is observed) at an angle? anybody? —Preceding unsigned comment added by 89.218.46.165 (talk) 14:58, 22 October 2007 (UTC)

## Blue Jays/Indigo Buntings are black

Someone should add that somewhere. I don't see that anywhere! ;) --HoopoeBaijiKite 18:29, 26 June 2007 (UTC)

## Momentum of a refracted ray

Apparently there is a paradox here some say could be p= nE/c (Hermann Minkowski 1908)

Or p= E/(nc) (Max Abraham 1909)

where n= refractive index, E energy of light quantum, c= speed of light in vacuo.

Rudolf Peierls raises this in his "More Surprises in Theoretical Physics" Princeton (1991). Discussed in Nature vol 444 14 December 2006 p823-824 including experiments to resolve.

It's rare for physics to fall clearly and absolutely flat on its face and a discussion of this problem by an expert should be included in the main article.--Nick Green 19:55, 9 October 2007 (UTC)

## No equation?

This article needs some equations. —Ben FrantzDale 02:30, 4 November 2007 (UTC)

## Geometrical Optics

Do we need a more scientific explanation of this? Saying light changes direction due to a change in speed doesn't really explain the processes involved (and is effectively incorrect as the velocity only appears to change). I'm not suggesting an in depth essay with reference to quantum electrodynamics, but the oscillating dipole model could feasibly be included. Doctorp9999 (talk) 23:12, 23 November 2007 (UTC)

## Refraction effect

There is a very popular effect called Refraction, by the magician David Penn. In case someone is looking for it, I thought I should add it to the the article as a disambig link. It is a commercial effect, so I will understand if someone wishes to remove it, as potential spam. However, I understand it is the fourth best selling magic DVD in the world at the moment (though I have yet to find a valid source to confirm it). I should add that I am not benefiting from the sale of these DVDs, nor do I advertise these. I am just trying to help Wikipedia expand. StephenBuxton (talk) 18:27, 6 December 2007 (UTC)

KY3R4N —Preceding unsigned comment added by 78.149.111.200 (talk) 21:45, 27 January 2008 (UTC)

My opinion is that is is too far removed from the subject of the article to be potentially confused. Most people know about the optical effect, and someone searching for the magic effect would certainly not be confused by arriving at the optical article. Am I right? Feel free to discuss further if needed; in the mean time, I am being bold and removing the link. TWCarlson (talk) 13:07, 14 September 2011 (UTC)

## The 'Refraction in a Perspex (acrylic) block.' picture

It might be just me, but I think this picture is too vague, I can barely see what's the light source (I guess it's coming from the left side). I think we should get another picture like this (http://www.phys.ufl.edu/demo/6_Optics/A_GeometricOptics/HalfCircleRefraction.jpg sorry can't get a nice linkey) picture 131.155.108.56 (talk) 11:18, 9 May 2008 (UTC)

## Near perfect sphere

File:Einstein gyro gravity probe b.jpg claims to be caused by refraction, but I see nothing in this article that would account for this effect. --Pascal666 18:33, 15 May 2009 (UTC)

## Easier explanation

Look at image, or animation, of refraction and split velocity into horizontal (x) and vertical (y) component. Notice how horizontal (x) velocity changes.

It is smaller when ray travels into more dense space and vice versa. (There are more particles to slow down movement ...)

That way it is easier to grasp. 84.16.123.194 (talk) 12:33, 18 May 2009 (UTC)

## Light Physics RE Refraction

Alright now my mind is having trouble grasping the photophysical events happening during refraction: Consider light, in the form of particulate photons, pouring down their projected path (lets say, emitting from a flashlight) in a cylindrical shape. As it hits a transparent glass surface at, say, a 40o-from-horizontal angle, it becomes bent. (This is just an inquiry, I will not do the calculations) We know this is true.

However let's say it were a stream of physical particles, passing through a "transparent" liquid media from a vacuum. It would not bend--it would keep it's physical path through the liquid if no gravity or other forces enacted upon it.

So...what property of light conditions it to bend around a corner as the photon particles hit a transparent glass medium?

In my (visual-working) brain, this seems to be a property of a force of attraction, due to the fact that stream of photons on the acute-angle side hit first, and as the photons hit the medium on the opposite side of the cylinder later, they become more attracted to the more numerous photons that have concentrated on the acute-angle side (light slows down as it hits the glass, which might cause an "accumulation" of sorts of photons). This attraction can cause the entire cone of light to shift IMO.

Is this plausible, nonsense, or something else? What photophysical properties am I missing in my hypothesis or misunderstanding?

I apologize if this entry is inappropriate to Wikipedia talk pages, please contact me if it is. Bullercruz1 (talk) 16:45, 25 December 2009 (UTC)

Better to ask on the Wikipedia:Reference desk/Science. As the Talk Page is meant for discussing ways to improve the artilce it relates to.:-) Anyway, I think you have to consider light as waves not as photons in order for refraction to be easily understood. Perhaps Prism_(optics) may help. Then again, consider that as the 'photons' enter a denser medium they will slow down (as will EM waves) and this is the cause of the bending and refraction. --220.101.28.25 (talk) 11:49, 10 January 2010 (UTC)

#### Hubble red shift hypothesis

How about that the light interacts with the matter in some way that is proportional to the frequency of the light particles, being more in relation to the greater number of particles, but not reducing it's velocity of propogation. So the photon size is also related to the number of particles per reaction. And I'll give you a wild one where you suppose that the space of the universe is curved such that the farther away a source of light is the more it's light is refracted and the redder it gets. So how's that re the Hubble red shift?WFPM (talk) 22:50, 28 April 2010 (UTC).WFPM (talk) 22:53, 28 April 2010 (UTC)

## recovered from revert

I reverted an edit but the editor added some material that might be useful for someone else--Profitoftruth85 (talk) 17:46, 25 May 2010 (UTC)

## Light shining through clouds is not refraction

Refraction causes the rays of light in this image to appear at different angles
Light on air–plexi surface in this experiment mainly undergoes refraction (lower ray) and to a lesser extent reflection (top ray).

Concerning the caption: Sorry, but that is patently false (says me, a stranger on the internet). But seriously: the different angles observed in the photo are merely a geometrical effect of perspective. All rays can be followed back to the position of the sun in the photograph. This has nothing at all to do with refraction. — Preceding unsigned comment added by 192.12.184.7 (talk) 19:15, 24 August 2011 (UTC)

I agree with you. The image with the laser was replaced by the clouds picture, which is really beautiful, but not caused by refraction.
I'm going to revert the image. The one before was a clear example of refraction. (A source that proves me wrong would open the debate back up.) Nice catch - just one day after the image was changed! TWCarlson (talk) 12:31, 14 September 2011 (UTC)

## Rearranged images

I went ahead and put some images in a gallery at the bottom. I also put clear space below sections to leave room for the image so the alignment with between the image and text didn't get messed up. I still think the article is disorganized and could use some work, but it is better than before, in my opinion. TWCarlson (talk) 13:10, 14 September 2011 (UTC)

## Image

In the third image the angle of incidence is in fact π/2-θ, that is very confusing. --Chricho ∀ (talk) 00:00, 2 November 2011 (UTC)

## History

Some is given at Snell's law and History of optics, but this could be greatly expanded. -- Beland (talk) 21:20, 10 June 2012 (UTC)

## Incorrect use of the word waves at many places

This article is about the refraction of light and light is in the form of rays and not waves. So I think 'waves' should be replaced with 'rays' wherever necessary.Mangal.anukriti (talk) 17:31, 1 December 2012 (UTC)