What is Refraction: Definition and 749 Discussions

In physics, refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed.
For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equal to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the indices of refraction (n2 / n1) of the two media.

















{\displaystyle {\frac {\sin \theta _{1}}{\sin \theta _{2}}}={\frac {v_{1}}{v_{2}}}={\frac {n_{2}}{n_{1}}}}

Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelength of light, and thus the angle of the refraction also varies correspondingly. This is called dispersion and causes prisms and rainbows to divide white light into its constituent spectral colors.

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  1. maxelcat

    B Does a photon's energy change as it refracts?

    I believe that when a photon is refracted it slows. Why is it that the wavelength decreases but that its frequency stays constant? Does this imply that the photon has not lost any energy in the process of slowing down given that E=hf? Thanks
  2. maxelcat

    B What happens to a photon's energy when it is refracted?

    I believe that when a photon is refracted it slows. Why is it that the wavelength decreases but that its frequency stays constant? Does this imply that the photon has not lost any energy in the process of slowing down given that E=hf? Thanks
  3. vwoods316

    Finding critical angle: not sure which one is correct

    Attempt one: 1sin(35.8) = n2sin(90) n2=0.58 1.33sin(𝜃)=0.58sin(90) 𝜃_c=25.8 Attempt two: n1=n2/sin𝜃_c n1=1/sin(35.8) n1 = 1.7 sin𝜃_c = 1.33 / 1.7 𝜃_c = 51.57
  4. S

    Refraction of light when traveling from air to glass

    I don't know how to explain it in terms of speed. I know the speed will decrease but if the ray entering the glass at certain angle, let say 10 degrees, the speed will also decrease so what is the relation of speed to the fact that the light will bend or not when entering the glass? And the...
  5. E

    I Why Are Reflected Rays Often Ignored in Lens Studies?

    Hi, I am wondering why reflected rays are not considered with lenses? If a Ray strikes a surface another is reflected off that striking point; however, this is not added when studying lenses, only refracted rays are considered. Is there any law which gives the ratio of reflected and refracted...
  6. I

    I The speed of one photon through a transparent medium

    We know from double-slit experiments that singular photons behave like waves, so I expect that one photon would undergo refraction when entering, with an angle different than 90 degree, into water, glass or other transparent material. Is that true? If the refraction occurs, than the speed of...
  7. N

    I Speed of information in a medium

    I am aware of the explanation for light slowing down. From what I understand the EM field causes electrons in the medium to oscillate interfering with the wave and slowing its progress through the medium. The question I am asking is about a light source (or any source) that is turned on. If I...
  8. ace

    B Pfund's method for refraction

    I have looked through all the sources to ever exist for Pfund's method, yet I cannot understand why in the situation of having water on the Petri Dish, is there a 2nd black ring after the second white illumination (first in the center from the laser i assume?). What stops the second white...
  9. H

    White light passing through prism

    I don't really have any idea. I know that shorter wavelengths refract more on entry to prism; e.g. ultra-violet refracts more than infra-red, but I don't know why they don't join up again when speeding up on exit from the prism.
  10. R

    B Radio waves -- Tissue Refractive Index

    The refractive index of tissue is approx. 1.4 for light, but with with lower frequencies the refractive index decreases. What is the tissue refractive index for radio waves 1 Hz - 1 MHz?
  11. J

    I Is photon energy negative in a negative-index metamaterial?

    Negative-index metamaterials are engineered to have a negative relative electric permittivity ##\epsilon_r## and negative relative magnetic permeability ##\mu_r## so that the index of refraction ##n## is negative: $$n=-\sqrt{\epsilon_r\mu_r}.$$ The dispersion relation for photons travelling in a...
  12. DragonSpear

    B Shape of Lenses -- Why are they always circular?

    In a magnifying glass, the lenses are always circular. I don't understand why because no matter what shape the lense is, it doesn't deny its physical properties and refraction would still occur, so why are they so consistent on making circular lenses. I predicted that circular lenses may be...
  13. Bluesy

    I Light Refraction, Biconvex Lens, Diagram Help

    I've read that the refraction of light at the boundary of a medium can be described as follows: -a line of connected people marching. one side of the line enters mud, and slows down. This causes the non-mud side to pivot towards the slower side, which then causes the line to change direction...
  14. L

    B Does light ever go from the eye to the image?

    You can see from the picture that the teacher has circled the arrows which shows light coming from image to the eye, and drew it in the opposite direction saying the light goes from the eye to the image. The marking scheme of this paper only says the correct direction does not specify which is...
  15. Rymazon

    I Outer layer refractive index - total internal refection on waveguide

    I am interested in experimenting with AR lenses and one of the main technologies is a waveguide. They rely on total internal reflection, which needs light to go from a higher to lower refractive index medium. I am reading that current AR lenses use an outer layer with a lower refractive index to...
  16. J

    A Why does the free end refraction occur after Brewster's angle in TM?

    Thanks for reading my question, and i’m really sorry about my poor english. What i am wondering about is why does the free end occur after the incidence angle overcome the Brewster angle in TM wave? (The ray incident from vacuum to glass(dense medium)) i tried to interpret this phenomenon with...
  17. L

    Apparent depth of an object underwater

    I would know how to solve this problem if the person had been standing pratically above of the object underwater by using Snell's law and the approximation ##\sin(\theta)\approx\tan(\theta)## fopr ##\theta## small, but in this case I don't see how to find the angles ##\theta_1## and ##\theta_2##...
  18. Ahmed1029

    I Reflection, refraction, and Snell's law

    Where do the laws of reflection, refraction, and Snell's law come from in geometric optics? Are they derivable from basic laws of physics?
  19. Remixex

    Estimating the velocity of seismic waves through an idealized Earth

    Hello, this is a repost from a much less-clear question I posted before (link to question: https://www.physicsforums.com/threads/triangles-inside-a-circle-to-represent-raypaths-inside-an-ideal-earth.1011998/#post-6596165). It's kind of a loaded question, however it can be expressed as triangles...
  20. Remixex

    Triangles inside a circle to represent raypaths inside an ideal Earth

    I have managed to get some of the required distances and angles. I have the distance ##a##, the velocity inside the mantle, the total radius of the Earth ##R_t## as well as mantle and core radii. I have also figured out the angle of incidence, however I cannot get the refracted angle with the...
  21. L

    Position of the image of an object placed in water

    I tried using the formula for the refraction of a spherical lens ##\frac{n_1}{p}+\frac{n_2}{q}=\frac{n_2-n_1}{R}## consider each slab as a spherical lens with curvature ##R=\infty## and by doing that I get ##\frac{1.33}{10}+\frac{1.5}{q}=0\Leftrightarrow q\approx -11.3 cm##. Since the piece of...
  22. L

    Light incident on a sphere, focused at a distance ##2R##

    I used the equation for the refraction on a spherical surface: ##\frac{n_1}{p}+\frac{n_2}{q}=\frac{n_2-n_1}{R}##, where ##n_1=1## is the index of refraction of air, ##n_2## the index of refraction of the sphere, ##R## is the radius of the glass sphere, ##p## is the object distance which, since...
  23. mcas

    Estimate the following quantities from a graph of the refractive index of NaCl

    a) I managed to obtain some results that are roughly around what is given in the answers. Because \varepsilon_{st} and \varepsilon_{\infty} are values of \varepsilon_{1}, I used this approximation: n\approx \frac{1}{\sqrt{2}} (\varepsilon_{1}+\sqrt{\varepsilon_{1}^2})^{1/2} -> \varepsilon_{1} =...
  24. S

    Help understanding refraction in water

    I recently had some trouble understanding refraction but after I finally understood where I went wrong (thanks to the people on this forum) I went back to my old lecture notes because I thought that what I recently learned didn't fit right with something that had previously been presented in my...
  25. S

    Previous university exam problem on refraction (that I think is wrong)

    This is a question on a past exam at university. The answer was provided (for revision purposes and exam preparation) but I never understood it and it continues to frustrate me because even if I can't come up with the right answer to a problem, I'll at least 'get' (understand) the proper answer...
  26. Paige_Turner

    B Gravitational Lensing: Refraction or Something Else?

    It seems like a strong gravitational field acts like spacetime is denser in some sense. Light passing through a gravitational lens is delayed, just like in a glass lens (which refracts because it's denser than air).
  27. lemma28

    B Fermat's principle and refraction -- Possible misunderstanding

    Consider a light starting at A in media 1 and going in and out a media 2 (say shaped as a disk) with relative index of refraction n to arrive at point B (in media 1). Fermat's principle says that the path taken by the ray between points A and B is the path that can be traversed in the least...
  28. R

    Refraction of light question -- Flintglass submerged in oil

    Hello, hopefully the question made sense, it was hard to translate. i attached a photo about the question. I started with n1=1.4, sinΘ1=37◦ and n2=1.62 1.4(sin(37◦))=1.62sinΘ2 1.4(sin(37◦))/1.62=sinΘ2 arcsin(0.52)=31.34◦ Is it calculated correctly?
  29. Mr_Allod

    Reflection and Refraction in an Elliptical Imaging Mirror

    My thoughts so far: a. Since the critical angle occurs at the origin for the given parameters I would imagine that the maximum power reflected would be 100% since at the critical angle ##\theta_t = \frac \pi 2## and ##r_ {\perp} = r_{\parallel} = 1##. I do not know how I might go about finding...
  30. J

    Lens with different refraction index on each side

    So I am not really familiar with lens questions when there's 2 different refraction indexes. I tried using n1/p+n2/q=-(n2-n1)/R but it doesn't seem to work. p would be the actual location of the fly and q would be the virtual location, what the fish sees if I am understanding correctly. n1...
  31. H

    Calculating the Effects of Lens Closeness on Light Refraction

    I know what happens initially, calculated as follows. 1/∞ + 1/q = 1/50, q=50 1/-25 + 1/q = 1/-25, q= ∞ However, how do we know about the after when the two lenses get closer to each other?
  32. G

    Critical angle (symmetry of refraction) confusion

    Refraction has a symmetry; on going from glass to air light at the glass air surfaces refracts away from the normal. If you turn the light source around and make the former refracted beam the incident beam then its refracted angle will be the former incident angle. So at critical angle, do the...
  33. veraamorim

    What is the relationship between refraction and giant waves in Nazaré?

    The waves of Nazaré start because of a storm in the open sea. The winds cause a disturbance on the surface, transformed into energy. When the depth is great, the propagation of the waves (energy) is practically constant. As they approach the coast, therefore in shallower places, the wave length...
  34. H

    Phase lag of light in materials

    There are 5 fantastic videos in this website: http://www.alfredleitner.com/ He is a very good educator and it is also very good to see those authentic experiments and aparatus. Anyway, in the following one at exacly 8:00 minutes he says that the phase lag induced by the dipole is always 90...
  35. P

    Suspended particles and the index of refraction

    Do suspended sub-micron sized particles influence the index of refraction of a liquid?
  36. L

    What is the refraction index of liver?

    Ok, so i finished my lab for physics 2 today. It was on reflection, refraction, Snells law etc. During my study, i looked up the refraction index of glass via this link: https://en.wikipedia.org/wiki/List_of_refractive_indices i noticed it had refraction indexes for a number of things that do...
  37. J

    Why Does Light Form a Cone When Refracted in a Swimming Pool?

    The first sketch is what I assumed would happen, where the light beams bends. And the second is meant to depict the light forming a cone, which I don't understand. [Mentors provided help re-posting the image that was missing]
  38. F

    Why does the amount of Refraction depend on wavelength?

    I understand that electrons of a material have a natural frequency of vibration and the refractive index results from the phase difference between the incident light's field oscillations and the field oscillations of these electrons...
  39. K

    How Does Refraction Affect Perceived Fish Size Underwater?

    From This picture, I think the fish will be smaller but the problem is how small will it be? (Fish "L" is the image of fish "K") Let ##H## be the depth of fish "K", ##\theta## be the angle of eyes to y-axis and ##n## is the index of refraction of water.
  40. G

    Internal reflection equation question

    As you can see we have 3 media here. Only focus on the glass and coating medium. Assume an incident ray comes from the air medium and is refracted inside the glass and then it is refracted again in the coating medium. The x angle is the angle inside the glass medium. In this case, if the...
  41. L

    Refraction through different mediums: calculating multiple angles help

    1. I have calculated the first angle using Snell's Law and with subsequent proceeding angles I am uncertain whether my workings are correct since I have used basic laws of geometry that all internal angles of a triangle add up to 180 degrees and that alternate angles are equal to find proceeding...
  42. C

    Size of a light beam before and after Refraction

    The size of light beam is same or different before and after refraction from a medium. If same then why we can not prove from mathematical expression. If not same why?
  43. Jaffer2020

    Refraction of Light: Myth or Reality?

    In my latest 10th grade physics lesson, we were learning about the refraction of light. I decided to share what I knew about why light slows down in a vacuum, which is, in short, because the electric field of the electromagnetic wave exerts a force on the charged electrons of a medium, which in...
  44. K

    Calculate the focal distance of the duplicate

    The picture below shows a so-called chromatic doublet, which is designed to minimize chromatic aberration, ie the wavelength dependence of the refractive index of the glass. The first lens has a flat first surface and a concave second surface with radius of curvature R and index of refraction n1...
  45. Efeguleroglu

    I have a contradiction about refraction

    (Black one is the object and grey is its image.) We know from Snell's Law: $$ n_1\sin\alpha=n_2\sin\theta $$ And I have been said that: $$ a=b\ (1)\\\ and\\\ \frac{h}{h'}=\frac{n_2}{n_1} \ (2) $$ Let's begin. $$...
  46. K

    Find the refractive index for the lens and find the image distance

    A thin lens has an upper radius of curvature 𝑅1 and a lower radius of curvature 𝑅2. When the lens is completely surrounded by air, it has a focal distance 𝑓. The lens is then placed in the interface between air and water inside a vessel (see figure). Calculate the refractive index for the glass...
  47. A

    Brewster's angle, dipole radiation and refraction

    So I was wondering how it is possible that there will be no p-pol light reflected when the refracted light is at 90 degrees to the reflected light (so incoming light is at Brewster's angle). The Brewster's angle was explained to me by saying that the electrons in the medium radiate light...
  48. M

    Combination lens equation questions

    Homework Statement: Lens questions. Homework Equations: idk Hello, so I was wanting to use a laser beam and purchase a few lens' online for a project and wanted to get something similar to the image below, where i would end with a horizontal light ray i was wondering if anyone knows the...