The subfield of optics in which light propagation is approximated in terms of rays. It mainly includes reflection and refraction on surfaces.
Questions tagged [geometric-optics]
1496 questions
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Why are mirror images flipped horizontally but not vertically?
Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
Arlen
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173
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Why do sunbeams diverge even though the sun is much more than a few kilometers away?
Consider this picture of sun beams streaming onto the valley through the clouds.
Given that the valley is only (at a guess) 3km wide, with simple trigonometry and the angles of the beams, this gives the result that the position of the light source…
user56903
112
votes
8 answers
Is it possible to start fire using moonlight?
You can start fire by focusing the sunlight using the magnifying glass.
I searched the web whether you can do the same using moonlight. And found this and this - the first two in Google search results.
What I found is the thermodynamics argument:…
Calmarius
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72
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6 answers
Could a computer unblur the image from an out of focus microscope?
Basically I'm wondering what is the nature of an out of focus image. Is it randomized information? Could the blur be undone by some algorithm?
user273872
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If a lens focuses all incoming light to a point, how do we get 2D images?
How do lenses produce 2-dimensional images, if a lens bends all incoming rays of light to intersect at the focal point? Shouldn't this produce a single dot of light on a screen placed at the focal length?
This is basically the standard diagram that…
Kristin
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Virtual vs Real image
I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are.
A virtual image occurs the object is less than the focal length of the lens from the lens, and a real image occurs when…
Jonathan.
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47
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6 answers
Do people wearing glasses have different field of view than those who don't?
There is one thing I sometimes wonder about ever since I was a child.
Do people who wear eye glasses see objects in different size than those who don't?(Technically different size means different projected image size on the retina.)
For example do…
Calmarius
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45
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4 answers
How does Fermat's principle make light choose a straight path over a short path?
This is a thought experiment where I have made a "C" shaped hole inside diamond. The refractive index $(\mu)$ of diamond is 2.45. Say we shine a laser from top of the "C" as shown.
My calculations show that light reaching A can reach B in the least…
Rishab Navaneet
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Why are there shadows surrounding these underwater lights?
I took this picture of a water feature on campus at Caltech:
The lamps at the bottom of this pool have large, circular shadows surrounding them, but there are also bright rings of light surrounding those shadows. Since there are no obstructions in…
Geoffrey
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41
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1 answer
How is a (rifle scope) reticle in focus?
The lens zooms and focuses something very far away, yet the reticle inside the lens assembly is in perfect focus just like the far objects. How?
Mark Legault
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What is this sort of abstract rainbow?
Today I saw the phenomenon in picture below. It was not raining (at least nearby me). What can that be? What is the technical explanation?
Edit: Just seen today in Southern Brazil another circumhorizon arc, this time together with a halo. Really…
Diracology
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Is it possible to focus the radiation from a black body to make something hotter than that black body?
My previous question wasn't specific enough. I'll try to be more specific.
Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative power falls on on a m². Now if we use a lens with 1m²…
Calmarius
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33
votes
1 answer
Can one determine the speed of the rain from the shape of the rainbow?
I was watching the rainbow today and started thinking about the effects of the rain falling in different directions.
The idea I had was that normally we model rain drops as small spheres, and this gives a characterizing angle for the perceived…
Mikael Fremling
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32
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3 answers
A Rainbow Paradox
I was studying the phenomena of the formation of a rainbow. In my book, the following diagram is given:
So, the rays at the red end of the spectrum make a larger angle with the incident ray than the rays at the violet end of the spectrum. However,…
golden_hawk21
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30
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Why is angle of incidence equal to angle of reflection?
In the Law of Reflection, the angle of incidence is equal to angle of reflection. Why is this true? This is clearly true experimentally, but how does one prove this true mathematically?
Gamira
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