Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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What really cause light/photons to appear slower in media?

I know that if we solve the Maxwell equation, we will end up with the phase velocity of light being related to the permeability and the permittivity of the material. But this is not what I'm ...
26
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5answers
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Why glass is transparent?

Once I asked this question from my teacher and he replied "because it passes light", "and why it passes light" I asked and he said "because it is transparent". Same question again, Why glass is ...
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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 ...
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How are classical optics phenomena explained in QED (Snell's law)?

How is the following classical optics phenomenon explained in quantum electrodynamics? Reflection and Refraction Are they simply due to photons being absorbed and re-emitted? How do we get to ...
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5answers
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Why wet is dark?

When something gets wet, it usually appears darker. This can be observed with soil, sand, cloth, paper, concrete, bricks ... What is the reason for this? How does water soaking into the material ...
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4answers
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Why does the sky change color?

Why the sky is blue during the day, red during sunrise/set and black during the night?
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1answer
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Why does the refractive index depend on wavelength? [duplicate]

Why do different wavelength get impeded more or less when in different materials? Moving with the same speed, but a longer physical distance would imply that the fields oscillate less times in the ...
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1answer
488 views

Partially polarized light with jones vectors?

I have read that polarized light is treated by Jones vectors and that to treat partially polarized light you have to use Stokes vectors and mueller matrices. Nonetheless, the optics notes that my ...
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How does gravitational lensing account for Einstein's Cross?

Einstein's Cross has been attributed to gravitational lensing. However, most examples of gravitational lensing are crescents known as Einstein's rings. I can easily understand the rings and crescents, ...
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1answer
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Why can you see virtual images?

In optics it is widely mentioned real images are projectable onto screens whereas virtual ones can only be seen by a person. Isn't that contradictory? I mean in order to see the virtual image it has ...
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660 views

What longest time ever was achieved at holding light in a closed volume?

For what longest possible time it was possible to hold light in a closed volume with mirrored walls? I would be most interested for results with empty volume but results with solid-state volume may ...
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Explain reflection laws at the atomic level

The "equal angles" law of refection on a flat mirror is a macroscopic phenomenon. To put it in anthropomorphic terms, how do individual photons know the orientation of the mirror so as to bounce off ...
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Is it possible to witness a circular rainbow?

What conditions would make it possible to see a naturally occurring fully 360° circular rainbow? Would it even be possible?
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4answers
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What happens to light in a perfect reflective sphere?

Let's say you have the ability to shine some light into a perfectly round sphere and the sphere's interior surface was perfectly smooth and reflective and there was no way for the light to escape. If ...
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4answers
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Is one way glass possible?

I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
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2answers
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Why does one get an illusion as moon following him?

When you run or ride bike at night if you observe the moon you feel like he moves along with you as the same speed you are going. Why?
14
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4answers
42k views

Why does the road look like it's wet on hot days?

Often, I'll be driving down the road on a summer day, and as I look ahead toward the horizon, I notice that the road looks like there's a puddle of water on it, or that it was somehow wet. Of course, ...
3
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2answers
684 views

The Goos Hanchen shift mechanism

When the light is totally reflected in the interface between dense and less-dense medium, we know that the reflected beam will shift a little. Currently I have known the reflection coef r, will be a ...
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1answer
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Where is a good place to learn (classical) optics?

I need to learn basic optics for a high school academic competition. Does anyone know any good places, preferably free and online, to learn the basics of optics, like lenses, angles of incidence, ...
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3answers
213 views

Why can colors be mixed? [duplicate]

We can combine colored light, creating other colors, at least in terms of visual perception. But how it the result physically "a different color" - if it is at all? Or is all this not a physical ...
51
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6answers
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Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray in color? (What atomic characteristics determine the color?) What makes copper and gold have ...
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3answers
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How does light speed up after coming out of a glass slab?

As I learned today in School, my teacher told me that when light enters a Glass Slab it slows down due to the change in density and it speeds up as it goes out of the Glass Slab. This causes a lateral ...
18
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4answers
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Is it possible to observe interference from 2 independent optical lasers?

It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for ...
8
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5answers
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Interference of polarized light

Does polarized light interfere?
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3answers
305 views

How to understand holography and hologram

I've spent some time reading wiki etc. What I get now is that apart from the normal light amplitude information, holograms also record the phase information of light. But this is so difficult for me ...
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Why are color values stored as Red, Green, Blue?

I learned in elementary school that you could get green by mixing blue with yellow. ...
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3answers
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Why is it difficult to differentiate between interference and diffraction?

Why is it difficult to differentiate between interference and diffraction? Is it because we don't clearly understand how both of these phenomenon takes place? My thoughts: From an answer to one of ...
25
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1answer
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Why does paper become translucent when smeared with oil but not (so much) with water?

When I smear oil onto a scrap of paper and rub it in, the paper becomes quite translucent; but when I attempt the same with water it doesn't as much. Why?
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1answer
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How are photons “consumed”?

I have very little background in physics, so I apologize if this question is painfully naive. Consider the following thought experiment: an observer is in a closed room whose walls, floor, and ...
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Why are objects opaque?

I have been searching the internet for answers to this question, but haven't found a convincing one. I would appreciate any response. I understand why objects are opaque/black. For example when ...
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Free Optics Simulation Programs

I'm having an extremely difficult time finding an optics program that is easy to use and offers accurate physics simulations. I'm not asking for much, I just want to be able to simulate a laser going ...
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2answers
298 views

Fully destructive interference

I'm aware that this is somewhat of a frequently asked question (not only here), and i've dug through respective answer for a few hours before i decided to ask here. None of those answers helped me ...
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5answers
425 views

Trapping a lightray

Given a solid whose interior is a hollow sphere with perfectly reflecting mirrors. A small hole is drilled in the sphere and a photon is sent in at some angle. Will it always eventually exit through ...
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2answers
85 views

Why does electromagnetic refraction happen?

Why does refraction happen? In high school textbooks, it is stated that it happens because the speed that electromagnetic waves propagate in the media change. But why cant they continue propagating in ...
6
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3answers
767 views

Recently publicized experiment on destructive interference between two laser beams

Recently I've had several non-physicist friends ask me, independently of each other, about an experiment where two collinear laser beams destructively interfere along a certain length. Everybody wants ...
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4answers
320 views

Sign convention in optics

Why is the sign convention used in the derivation of the lens formula and yet used again when it is applied in numerical problems? Won't the whole idea of sign convention be eliminated if it is used ...
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Observing lunar lander and footprints on the moon?

After Apollo 11 first landed on the Moon in 1969, there have been conspiracy theories that this never really happened and that it was all a hoax. In 2010 NASA released photos from its Lunar ...
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2answers
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Why does sunset over a body of water cause a path of light stretching towards the horizon?

Have you ever notice the sunset's image in the sea? It's like long light path to the end of the horizon! I've attached a sample of this: How can we explain this? I know that it can happen even in ...
9
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1answer
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Two mirrors facing each other

What happens when you place two mirrors facing each other? Is it possible to have an infinite amount of reflections?
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How to bend light?

As we all know that light travels in rectilinear motion. But can we bend light in parabolic path? If not practically then is it possible in paper? Has anyone succeeded in doing that practically ?
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2answers
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Maximum theoretical bandwidth of fibre-optics

Ignoring hardware at either end and their technological limitations, what is the maximum theoretical bandwidth of fibre optic cables currently in use / being deployed in a FTTH type situations? I ...
5
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2answers
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Is manufacturing roughness really the only reason we don't see optical interference in thick dielectrics like windows?

I had always kind of wondered why we didn't see interference in things like windows -- we were taught that the condition is that the thickness of the film/slab/medium just has to be an integral number ...
5
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2answers
364 views

How do you calculate power at the focal point of a mirror?

I'm a Mechanical Engineering student and I'm working on my senior project, so I need help. My project is about designing a solar dish having a diameter of 1.5 meters and a focal length of 60cm. so at ...
2
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3answers
157 views

What really makes a rainbow happen?

Yes, a rainbow is formed when a raindrop refracts light, but why then does the whole sky not become a huge rainbow when it rains? Would the light not be dispersed into ordinary 'white' light? What ...
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2answers
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Why the light bent towards the normal when they pass from rarer medium to denser medium?

Whenever the light rays are entering the rarer to denser medium they bend toward the normal. Then why the rays choose the path toward the normal? Why it cannot choose the path away form the normal?
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Do gravitational lenses have a focus point?

Do gravitational lenses have a focus point? Could I burn space ants?
9
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7answers
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Why does a laser beam diverge?

I was wondering why a laser beam diverges. If all the photons are in the same direction, I would imagine that it would stay that way over a long distance. I am aware that a perfectly collimated beam ...
7
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2answers
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Photon energy - momentum in matter

$E = h\nu$ and $P = h\nu/c$ in vacuum. If a photon enters water, it's frequency $\nu$ doesn't change. What are its energy and momentum : $h\nu$ ? and $h\nu/c$ ? Since part of it's energy and momentum ...
2
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3answers
337 views

How Does $\epsilon$ Relate to the Dampened Harmonic Motion of Electrons?

I realize that the permittivity $\epsilon$ of a substance is easily calculated based on diffraction angles, but I am not satisfied with merely measuring it experimentally. I wish to understand its ...
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6answers
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How come an anti-reflective coating makes glass *more* transparent?

The book I'm reading about optics says that an anti-reflective film applied on glass* makes the glass more transparent, because the air→film and film→glass reflected waves (originated from a paraxial ...