What is Geometrical optics: Definition and 53 Discussions

Geometrical optics, or ray optics, is a model of optics that describes light propagation in terms of rays. The ray in geometric optics is an abstraction useful for approximating the paths along which light propagates under certain circumstances.
The simplifying assumptions of geometrical optics include that light rays:

propagate in straight-line paths as they travel in a homogeneous medium
bend, and in particular circumstances may split in two, at the interface between two dissimilar media
follow curved paths in a medium in which the refractive index changes
may be absorbed or reflected.Geometrical optics does not account for certain optical effects such as diffraction and interference. This simplification is useful in practice; it is an excellent approximation when the wavelength is small compared to the size of structures with which the light interacts. The techniques are particularly useful in describing geometrical aspects of imaging, including optical aberrations.

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  1. Florian Geyer

    Help with a Refraction problem that involves light passing through different media

    Hello esteemed members, I hope this message will find you well, I have encountered this problem in Serway and Jewitt 9e. My problem is only with parts (d) and (e). I tried to solve the problem in two ways, one is based on intuition, and the second is based on the equations, but the two method...
  2. Hak

    Mirror system in geometrical optics

    I tried solving it in this way, distinguishing 3 cases and passing the first ray through the point located at a greater distance from the vertex of the angle formed by the two mirrors: 1) the angle of incidence of the ray on the mirror inclined 45° to the horizontal is 45° or 0°: in the first...
  3. Anish Joshi

    B Geometrical Optics: Explaining the Effects of Small Wavelengths

    Read this in my textbook:- The reason Geometrical optics works in case of formation of shadows, reflection and rarefaction is that the wavelength of light is much smaller compared to the reflecting/refracting surfaces as well as shadow causing objects that we use in day-to-day life. I...
  4. tomceka

    Geometrical optics: using Snell's law, find the depth of the pool

    α=30°; l=0.5 m; n1=1; n2=1.33 α+β=90°, so β=90°-30°=60°. Using Snell's law: sinβ/sinγ = n2/n1 sinγ≈0.651 γ≈41°. β=γ+θ (vertical angles) θ=60°-41°=19° tan(θ+β)=l/h h=l/tan(θ+γ) h=0.5/(tan(19+41))≈0.289 m
  5. Marioweee

    What is the focal point of a lens in a geometrical optics problem?

    I have recently started with geometric optics and I do not quite understand what this problem asks of me. According to the statement, the focal point of the lens would be -25.5cm, right? That is, it is only a problem of concepts where it is not necessary to take into account the radii of the...
  6. nish95

    Final Image position for a setup with two lenses

    First image is an object for the concave lens so won't +ve direction change from right to left?! In that case, object distance will be -ve (from concave lens towards right side). Any ideas? Solution in the book takes first image's distance to be +ve. See attached ray diagram for clarification...
  7. I

    Geometrical Optics - Light ray angles on a spherical mirror

    I can't see how the textbook produces the following relationships between angles: $$ \theta = \phi + \alpha \qquad (1)$$ $$ 2\theta = \alpha + \alpha ' \qquad (2)$$ My thinking is that the exterior angle theorem for triangles was used to create expression ##(1)##, but I am unsure as to how...
  8. K_Physics

    Relative Intensity of Various Light Sources - Lab Experiment

    Homework Statement I've linked my data table down below. My problem is the relative intensity column. From the table, the units of relative intensity are w/m/s. I'm assuming this is power/velocity, where velocity is the speed of light. However, nowhere in the lab manual did it mention the...
  9. shihab-kol

    The tangent and perpendicular of a mirror

    The tangent passes through just one point Now i can draw it such that the angle of incidence is always 0 and incident angle is always 90 Then no image will be formed. Why does this not happen??
  10. shihab-kol

    Centre of curvature of a mirror and the perpendicular

    If the normal is always 90 to the mirror can we assume that it always passes through centre of curvature? The light rays passing through the centre are reflected back in the same direction as angle of incidence is 0 and incident angle is 90 so, the normal should pass through the centre.
  11. Marcus95

    Biconvex Lens Floating on Mercury

    Homework Statement A thin bi-convex lens with refractive index n has spherical surfaces with equal radii of curvature r and measured focal length f. The lens floats horizontally on the surface of liquid mercury so that its lower surface effectively becomes a spherical mirror. A point object on...
  12. A

    Geometrical optics, refraction

    Homework Statement A spherical surface of roc 10 cm separates 2 media x and y of refractive indices 3/2 and 4/3 respectively. Centre of the spherical surface lies in the denser medium. An object is placed i x medium. For image to be real, the object distance must be ---- A) >90 cm B) <90 cm...
  13. F

    How Deep Does the Acrylic Bottom Appear Under Water?

    Homework Statement A container with a layer of water (n=1.33) of 5 cm thick is over a block of acrylic (n=1.5) of 3 cm thick. An observer watches (perpendicularly from above) the lowest surface of the acrylic. What distance does it (the bottom surface) seems to be from the top of the water...
  14. T

    Displacement of virtual image problem

    An object is within a glass sphere of radius R with a refractive index of 1.5 . I'm trying to calculate the displacement of the virtual object relative to the actual when viewed from the side, such that the refracted ray emanating from the object becomes horizontal. I would like to know S (the...
  15. A

    Geometrical Optics: Image Position with No Principal Axis

    What would be the position an image formed by a Lens or a mirror if the object is not kept on the principal axis?
  16. isnainidiah

    Geometrical Optics: Explaining Concepts with Fermat's Principle

    How do you use Fermat's principle of least time to explain various concepts in geometrical optics?
  17. isnainidiah

    Why we use wavelength to divided into ray, wave and particle

    I want to ask something about light, light can be defined as ray, wave, or particle. The group formed because of the wavelength, if the wavelength is less than the dimension of equipment it is grouped into ray, if the wavelength is equal to the dimension of equipment it is grouped into wave, and...
  18. Christian Grey

    Astrophysics uses wave optics or geometrical optics?

    I know Astrophysics uses concepts like relativity etc. But I want to know does it uses wave optics or geometrical optics? The phenomenon of light,wave optics(reflection,refraction,polarization,diffraction and interference) that we see everyday, is used in Astrophysics? Or does it uses...
  19. K

    Picture of Bragg's diffraction sounds confusing

    This may be a little of a stupid question. But I was looking at a diagram describing Bragg's Law of Diffraction. and I was like...how can an interference happen if wave beam C and wave beam C' are hitting different points on the detector screen?! they are not hitting the same point on the...
  20. norlesh

    Would a flattened (sheet glass) dispersion prism work?

    Could a thin sheet of glass with appropriate edge angles work as a dispersion prism? If the prism were laying flat my thoughts are the light should be contained via TIR in a plane that would remain perpendicular to the top and bottom while said plane dispersed horizontally according to...
  21. S

    The ratio of the distance of the focus and the point

    1. The problem statement: A ray of light is incident on a concave mirror. It is parallel to the principle axis and its height from principle axis is equal to the focal length of the mirror. the ratio of the distance of point B to the distance of the focus from the center of curvature is( AB is...
  22. S

    The time span for which insect can see its image?

    1. The problem: A plane mirror of length 2m is kept along the line y=-x as shown in the figure. An insect having velocity of 4 cm/s is moving along x-axis from far away. The time span for which the insect can see its image will be:A)50 sec B)25 sec C)25√2 sec D)50√2 sec 2.The answer...
  23. Archit Nanda

    Optics -- caustic curve equation

    I went through this article: http://users.df.uba.ar/sgil/physics_paper_doc/papers_phys/ondas_optics/caustica1.pdf But I think that when we do F=0, we are assuming the centre of the curve to be the origin and assuming the curve to be a circle, because only then will we be able to say that OP=ON...
  24. D

    Application of advanced spectrometer in geometrical optics?

    We have an advanced spectrometer in our geometrical optics lab! I'm seeking for any experiment in geometrical optics to include it!
  25. K

    Off-Axis Mirror Collimated Beam Contour

    When you collimate a point source using an off-axis parabolic mirror (OAP) with a circular shape, the beam area of the collimated light becomes more and more elliptical (x-dir. is smaller than y-dir.) as the off-axis angle is increased. Is there a reason why this happens? And is there a way to...
  26. Choisai

    Microscope magnification with camera

    I have two lenses for my microscope. The object lens which magnifies 63 X. Then there is my eyepiece lens with f=100 mm which focuses the incoming light at an camera. How can I calculate the total magnification? All calculations so far for the eyepiece involve the 25 cm of the human eye, but now...
  27. J

    Does anyone know of a simple eye simulator? (geometrical optics)

    I'm looking for a "simple" calculator, most likely a matrix based thing, to allow me to work out the size of an image projected on the retina by an object of a given size some distance from the retina. being the eye, the thin film approximation is no good (i.e. if I have an object 3cm from the...
  28. D

    Geometrical optics- position of image

    Homework Statement A sphere of radius 12.0cm has refractive index of 1.33. A speck is 4.0cm from the centre of the sphere is viewed along the diameter that passes thru the speck. Find the position of image when the speck is viewed from the nearer side? the ans is -7.2cm Homework Equations...
  29. H

    What is the Distance d in Snell's Law and the Pythagorean Theorem?

    In the following diagram find the distance d if a=4.0 mm, Θ=30° n_asinΘ_a=n_bsinΘ_b: snells law a^2+b^2=c^2: pythagorean theorem I think I got the angle to the problem correct. I am not sure if this is correct. Is this correct Θ_b=sin^-1(1sin30/1.52)?
  30. H

    Finding Refraction Angle and Wavelength in Water for Sodium Light?

    A narrow beam of sodium light (λ=5893 A) is incident from air on a smooth surface water at θ=35°. Find the refraction angle and wavelength in water. n=λ_0/λ:wavelength of light in a material n_asinΘ_a=n_bsinΘ_b: snells law n=c/v:index of refraction I tried using the wavelength of light...
  31. D

    How High Should the Mirror Be Placed for Full Reflection?

    Homework Statement A man stands 1.85m in front of a mirror hanging on a wall. His eyes are 10 cm below the top of his head. At what height from the floor, must the mirror be placed? Homework Equations Snells Law: n1*sin(omega)1=n2*sin(omega)2 The Attempt at a Solution I converted...
  32. W

    Matlab code for geometrical optics

    Hello all, i have frustrating task in my lab... i have to generate a code in MATLAB that will get the focal length and the object distance from the lens, i.e image (1000X1000 pixels). transfer it through the lens and, for the output it should be the result of it...
  33. S

    Geometrical Optics (lens and refraction)

    Homework Statement 1. A cylindrical tank 2.4 m deep is full to the brim with water. Sunlight first hits part of the tahnk bottom when the rising maes at 22o angle with the horizon. Find the tank's diameter 2. An aquarium is made from a thin-walled tube of transparent plastic 50 cm in...
  34. F

    Geometrical optics - lens floating in mercury

    Homework Statement Consider a thin bi-convex lens with refractive index n which has spherical surfaces with equal radii of curvature r and a measured focal length f. The lens floats horizontally on the surface of liquid mercury so that its lower surface effectively becomes a spherical mirror...
  35. F

    Gaussian beam and focusing versus geometrical optics

    Hello Forum, if we take a Gaussian beam whose waist occurs at the front focus of a positive lens, we will see that the Gaussian beam will have another waist at the back focus of the lens... That seems to be in contradiction with what happens in geometrical optics: if we place a point...
  36. Z

    Miscellaneous Geometrical Optics Questions

    Homework Statement I have two problems- 1) A plano-covex lens is silvered on its plane-side and then it acts like a concave mirror of focal length 20cm. When the convex side is silvered it acts like a concave mirror of 7 cm focal length. What is the refractive index of the lens? 2) A...
  37. fluidistic

    Geometrical optics, lens and image

    Homework Statement What should be the focal distance of a negative thin lens such that there's a virtual image situated at 50 cm from the lens, of an ant at 100 cm from the lens? Given that the ant is at the right side of the lens, localize and describe the image. Homework Equations...
  38. A

    How does the presence of water affect the image formed by a converging lens?

    Homework Statement A needle of length 5.0cm placed at the bottom of a beaker and a converging lens of focal length 20.0cm is held 30.0cm from the needle.The needle is illuminated with a lamp from the bottom.An image of the needle is formed on a screen.The beaker is now filled with...
  39. B

    Are These Geometrical Optics Diagrams Correct?

    I had to draw these diagrams for an AP Physics summer work assignment. I was just wondering if someone could look them over and let me know if I did them correctly. Thanks! http://img356.imageshack.us/img356/5520/go1kf2.png" http://img354.imageshack.us/img354/8011/go2lj2.png"
  40. K

    Geometrical optics LENSES Refraction

    Homework Statement A lens is made of glass for which the refractive index is n[r]=1.5 for red beams and n[v]=1.52 for violet beams. radii of both surfaces are the same and equal R=1m. Find the distance between foci for red and violet beams Homework Equations The Attempt at a Solution
  41. A

    Geometrical Optics: Solving 2 Prism Problem

    http://img140.imageshack.us/my.php?image=jonesf2238vg1.gif Problem Statement: Two prisms with the same angle but different indices of refraction are put together to form a parallel sided block of glass (see the figure). The index of the first prism is n1 = 1.48 and that of the second prism is...
  42. I

    Do You Find Geometrical Optics Frustrating?

    do you hate it to? note this is not an anonymous ballet in case someone votes the second option so that i can berate them.
  43. J

    Geometrical Optics: Image of Object 2m Away From Convex Mirror

    Homework Statement An object is located 2 m away from a convex mirror with radius of curvature of 1 m. (a) Draw the ray trace diagram (observe scale!) and use that to deduce where the image occurs (b) What is the distance between the image and the mirror? (c) Strike out that which is...
  44. J

    Geometrical Optics: Explaining 2 Focus Positions

    Homework Statement Explain why for a given object screen distance there are two positions where the image is in focus. Is this always true? Homework Equations The Attempt at a Solution
  45. C

    Geometrical Optics: Construct Ray Paths for Lens-Mirror System

    A convex lens of focal length f is placed in front of a convex mirror having the same principal axis as the lens. Construct the path of a ray of light which coincides with the corresponding ray emerging from the lens-mirror system, and the path of the ray whose corresponding emergent ray is its...
  46. P

    What are some hints for solving Geometrical Optics problems?

    I'm having some trouble with a couple of Optics questions, any hints would be much appreciated! THe first quetion states that a concave mirror forms an image on a screen twice as large as the object. The object and the screen are then moved such that the new image produced is 3x's the size...
  47. S

    Can Geometrical Optics Queries Be Shared More Effectively Than in ZIP Files?

    I have my question,doubt and solution in the attachment that followed.Thanks for anybody that spend some time on this question.Sorry to say that the file format is *.zip .
  48. S

    Question on geometrical optics

    I have my question,doubt and solution in the attachment that followed.Thanks for anybody that spend some time on this question.Sorry to say that the file format is *.zip .
  49. G

    Design Achromatic Lens: Crown & Flint Glass, Focal Length 100cm

    Hey guys and gals...i am really stuff on dis question.. n i really need 2 knw homework 2 do dis.. so ne1 please help..n post der views...cheers! Design a converging achromatic lens of focal length 100cm. Refractive indices and dispersive powers for the two glasses available are 1.51 and 0.016...