Geometric optics Definition and 75 Threads

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. Darth Frodo

    How Does Lens Focal Length Affect Image Size on a Wall?

    Problem 1 A flat screen TV is place on a wall in a room. A lens of focal length 50cm is placed between the television and the opposite wall so that a sharp image with one quarter of that of the area of the television is produced on the opposite wall. Answer: Magnification =...
  2. P

    Sign convention in geometric optics.

    Until today I learned in geometric optics that Object distance +ve for real object else -ve Image distance +ve for real image else -ve Radius of curvature +ve for if light comes to the surcace from the side lying center of curvature else -ve On the basis of this the lens formula...
  3. S

    What Focal Length is Needed to Project a 35mm Slide onto a Large Screen?

    Homework Statement A 35mm slide(picture size is actually 24 by 36 mm)is to be projected on a screen1.80m by 2.70 m placed 7.50m from the projector. What focal length lens should be used if the image is to cover the screen?Homework Equations the only equation i can think of is the lens equation...
  4. K

    Geometric optics and photography

    Hi there, I have a question about photography. We know that in geometric optics, a bunch of parallel rays which going into the len will focus on the focus (a point). But as we see, the image is a set of points on a 2 dimensional plane. It is quite confusing that a focus is only a point...
  5. C

    Solve Geometric Optics: Convex & Concave Lenses, Focal Lengths

    Homework Statement Given a convex lens of focal length of (x+5) cm and a concave lens of focal length x cm. The 2 lenses are placed 30 cm apart coaxially i.e along the same axis with the convex lens on the left while the concave lens is on the right. A light bulb is placed to the left of the...
  6. A

    Actual truck speed (geometric optics)

    http://img691.imageshack.us/img691/5753/98144291.jpg this is the solution found in the solution manual, http://img693.imageshack.us/img693/6536/67143924.jpg I didn't understand the part of taking the derivative part, that is how does this http://img22.imageshack.us/img22/8125/87467649.jpg...
  7. C

    Geometric Optics: A Diverging and Converging Lense in Series

    A romantic, lighted candle is placed 39 cm in front of a diverging lens. The light passes through the diverging lens and on to a converging lens of focal length 10 cm that is 5 cm from the diverging lens. The final image is real, inverted, and 21 cm beyond the converging lens. Find the focal...
  8. S

    Geometric Optics- Refraction , reflected ray's

    Homework Statement A beam of light in air makes an incident angle with the normal at 53 with an unknown substance. Part of the light is relected and part is refracted into the substance. The reflected ray and the refracted ray make an angle of 90 degrees. a) What is the refracted angle...
  9. S

    Geometric Optics: Snell's Law calculation problem

    Homework Statement Calculate the angle of incidence for an angle of refraction of 10° for a) Diamond (2.42) to air θ2=Angle of refraction=10° n2=Index of refraction on refractive medium=1 n1=index of refraction on incident medium=2.42 θ1=? Homework Equations n1sinθ1=n2sinθ2...
  10. M

    Geometric optics - why pinhole bends rays like lens

    We were discussing in an https://www.physicsforums.com/showthread.php?t=284322" that pinholes work like lenses, in that they form inverted real images. The other day, a friend told me, that pinholes even do bend the light rays like a lens do. I can - as being nearsighted - actually use a pinhole...
  11. M

    Geometric optics - why inverted image from thin lens

    Three questions: 1) Anyone have a pedagogic answer to why the image formed by a thin lens is inverted (i.e. upside-down)? I realize that to get a focused image, the lens has to converge the rays one way or another, so then, eventually, the rays have to cross the optic axis, which in turn...
  12. A

    How Does a Mooney Rhomb Convert Linear Light to Circular Polarized Light?

    Homework Statement A Mooney rhomb is a quadrilateral prism that converts linear light to circular polarized light. The question is here...
  13. G

    Critical Angle Geometric Optics

    There is a still-water lake and air interface. Light travels from the water to the air so that the incident angle is also a critical angle, making it so that the light runs along the surface of the water. Considering that this ray is reversible (air to water), a fish looking up at the surface...
  14. B

    How Does a 30-Degree Tilted Mirror Affect Viewing a Full Body Image?

    Homework Statement If a plane mirror is hung at an angle of 30 degrees from the vertical toward the viewer. what is the minimum length that will allow the viewer to see the full body image if the line of vision can not be depressed below the horizontal. you may assume that the eyes are at the...
  15. T

    What Causes Light to Bend in Gradients?

    I'm sure many of you guys have seen the videos of a beam of light (namely a laser of some sort) pass through a volume of liquid in which there is a gradient of index of refraction from the bottom of the tank to the top. Think of a sugar solution in which more sugar collects at the bottom and...
  16. C

    Geometric Optics: Can Virtual Objects Form Images?

    is it possible to have an virtual OBJECT in image formation?
  17. N

    Need help understanding wording of simple geometric optics problem

    I understand the material this problem is based on very well, but I feel very sad when I read this problem because it makes very little sense to me. I'm hoping it's just me that's confused by it and not everyone else - because in that case I should be able to get help here. Here is the...
  18. P

    Geometric Optics- Two Questions

    1.Determine the magnification of a 5cm object that has been placed 20 cm in front of a lens with a power of -2.5 d? 2. Light strikes a rectangular piece of crown glass with an angle of incidence of 30 degrees. If the block of glass is 10cm, determine the measure of lateral displacement. Can...
  19. P

    Geometric optics vs Electromagnetic waves

    Light which are electromagnetic waves have an electric field component and magnetic field component. The electric field can be phase shifted but the magnetic field never does. In geometric optics, light is modeled as a straight line and its rules upon reflection and refraction are according...
  20. M

    Can Geometric Optics Help Solve These Light Refraction Problems?

    In my first two of weeks we covered most of the light unit, and i was sick(in class, but coulnd't focus or abosrb information) and now i am at the end of the unit with this due tomoro and i do not understand how to do any, I need to learn how to do this, I can't understand most of it right...
  21. E

    Solving Geometric Optics Problem: Raising Height of Camera

    Here's a question that everyone in my class that I talked to couldn't find an answer to. "Suppose that you focus a camera direclty down on a printed letter on this page. The letter is then covered with a 1.00mm thick microscope slide (n = 1.55). How high must the camera be raised in order to...
  22. S

    How Does Aperture Size Affect Exposure Time in Photography?

    Hello! I'm having difficulty answering the following question: Camera A has a lens with an aperture diameter of 8.50 mm. It photographs an object using the correct exposure time of 3.33×10−2 s. What exposure time should be used with camera B in photographing the same object with the...
  23. L

    How Does Light Behave When Passing Through Multiple Lenses?

    Two lenses, one converging with focal length 20cm and one diverging with focal length -10cm, are placed 25cm apart. An object is placed 60cm in front of the converging lens. Determine (a) the position and (b) the magnification of the final image formed. I have a problem with this becasue...
  24. L

    Answer Geometric Optics Problem: Find Reflection Angle for Index > 1.42

    Hey guys! I need some helps on an optics problem. It is from Giancoli Chapter 23, question 41: Question: A beam of light enters the end of an optic fiber (attachment B). Show that we can guarantee total internal reflection at the side surface of the material (at point a), if the index of...
  25. R

    Archived Telescope geometric optics problem

    Ok I'm working on my geometric optics homework and this is the last problem and I can't seem to get it right. An 6 astronomical telescope has a 32 cm focal-length objective lens. After looking at stars, an astronomer moves the eyepiece 1.0 cm farther away from the objective to focus on nearer...
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