45 votes
Accepted

Why does the light passing through a prism get bent in the same direction twice?

The normals in consideration for the incident and emergent rays are different. For simplicity, take a monochromatic beam of light incident on a prism, as shown in this figure: When light is incident ...
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35 votes

Can you actually stand inside a rainbow? I see people claiming you can

It's impossible to "stand inside a rainbow" because there is no such place. A rainbow (or, more accurately, a series of rainbows) is the result of multiple reflections from light rays coming ...
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  • 4,323
35 votes

White full moon reflected orange-red light off of Atlantic Ocean surface. Why is this?

You would probably be about 9 to 12 km high, above the bulk of the atmosphere. The blue part of the light from the moon is more diffused travelling through the atmosphere and back, leaving the red ...
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29 votes
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Spherical mirrors or parabolic mirrors?

Well, the mirrors you are learning in physics are spherical. There are both spherical and parabolic mirrors. The only difference between them is that parabolic mirrors are more precise; they have only ...
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29 votes

Can you actually stand inside a rainbow? I see people claiming you can

A rainbow is formed by the reflection and refraction of light from the Sun by water droplets. This is illustrated in the diagram below. The process by which this happens is fairly involved and there ...
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25 votes

Why does the wave velocity of EM signals in a wire depend on the insulator's permittivity?

As it turns out, the currents and charge density oscillations in the metal wire are not the only parts of the wave. There are also the fields! And where are the fields? Well, if the wire is a good ...
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22 votes
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Where does the "water" come from in a mirage?

The reflected image of the palm tree is accompanied by the reflected image of the sky above and surrounding it. so in the reflection, you see the palm tree and the sky. There is no pool of water: the ...
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22 votes

Can you actually stand inside a rainbow? I see people claiming you can

In a sense, you can. Though that might not mean quite what you think it does. It is a bit like standing in the beam of a flashlight. The video you linked shows this happening - Drove Through the End ...
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  • 27.7k
19 votes
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Can we bend a light ray into any closed loop?

Let's try to design an axisymmetric medium in which a concentric circle of radius $R$ is a possible light ray. The index of refraction is $n(r)$. In polar coordinates, light rays close to the desired ...
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  • 3,540
15 votes
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Was Einstein's General Theory of Relativity wrong?

The claim is incorrect. General relativity passes all of those tests and many more. In particular, many of the measurements of the deflection of light near the sun are made using VLBI with radio ...
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  • 69.1k
14 votes

Where does the "water" come from in a mirage?

The water doesn't appear, we generally consider reflections on the ground to be some water body, as we don't generally have shiny surfaces on roads or deserts. So the reflection is often mistaken for ...
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13 votes

Why does the light passing through a prism get bent in the same direction twice?

This is how refraction of light in a medium works. The phase velocity $v$ of light changes transitioning from one medium to a different density medium according to its refraction index $n$ and the ...
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  • 3,186
9 votes

Why does the wave velocity of EM signals in a wire depend on the insulator's permittivity?

In a transmission line (and in fact in all circuits) electric energy is actually transmitted as electromagnetic waves whose energy is concentrated in the space between the wires. In a transmission ...
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  • 9,458
8 votes

Can we bend a light ray into any closed loop?

Ok so here are my thoughts. I wanted to construct something like a clock where each circular sector is made of a different material. The incoming angle of the light ray with respect to the boundary of ...
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  • 1,199
8 votes
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Why does sunset spread over the horizon?

At sunset the sunlight that we can see passes through a large (many hundreds of kilometers) distance inside the atmosphere. As it propagates, part of it gets scattered away due to Rayleigh scattering. ...
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8 votes
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How do we perceive object distance in refraction/reflection?

After reflection the rays seem to be coming in the direction that they would if there were an object on the left. image from here The brain chooses the most likely cause for the rays to be coming in ...
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  • 13.4k
8 votes

Can you actually stand inside a rainbow? I see people claiming you can

A rainbow is a result of geometric optics. The sun needs to be behind or overhead and rain droplets in front of you. The main rainbow is caused by refraction at air-water interfaces and one reflection ...
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6 votes
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Reproducing the disappearing glass experiment with normal glass

If the glass rod is surrounded by a liquid that has the same index of refraction, the speed of light will not change as it enters the rod meaning there'll be no refraction. If there is no refraction, ...
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  • 25.6k
6 votes

Apparent error in Snell-Descartes' law in the case of refraction - what am I missing?

The apparent location of an object is where it would be if the light rays had traveled in a straight line from the object to your eyes. The rays actually bent downward at the water's surface, and came ...
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6 votes
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How to derive this angular shift formula, $\lambda_\theta=\lambda_0\left[1-\frac{\eta^0}{\eta^*}\sin^2\theta\right]^{1/2}$ for interference filters?

For the purpose of the question, I find it helpful to formulate the laws of refraction in terms of wave vectors $\vec k$. With it a plane wave (which we are assuming here) can be easily described by a ...
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  • 6,930
6 votes
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Why does light bend when it enters a medium?

Those equations are written for the $E$- and $B$-fields at the boundary. The $E$-field has a discontinuity at the boundary, but the $B$-field is continuous at the boundary, and this can be deduced by ...
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5 votes

How can you explain refraction of a single ray of light while entering in denser medium from rarer?

There is no such thing as a single ray of light. They are not countable entities. Ray optics is an approximation to Maxwell’s equations over length scales that are much larger than the wavelength. So ...
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  • 69.1k
5 votes

How does the combination of lens create a sharper image?

It's hard to answer without knowing the context of the statement. But generally, multiple lenses can reduce aberrations. Real lenses aren't perfect, and images suffer because of that. Rays ...
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  • 21.4k
5 votes

Can you actually stand inside a rainbow? I see people claiming you can

You can stand inside a rainbow, there is even a photo of someone doing so on Wikipedia: The nuance of it is that in that picture, the person photographed probably does not see the rainbow around them....
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4 votes

Question about refraction in a swimming pool

Generally when you’re underwater and look straight up, you do not notice your reflection. It’s there, but drowned out by all the light coming through from above. For the same reason, you don’t see ...
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  • 9,221
4 votes

Spherical mirrors or parabolic mirrors?

Either there was some qualification that you missed, or your physics class is being overly simplistic. I don't know whether you've taken Calculus yet, but in Calculus terms, spheres and parabolas are ...
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4 votes

Can we bend a light ray into any closed loop?

OP seems to be asking about the case that uses a smoothly varying isotropic refractive index $n({\bf r})$ with no jumps and with no reflections/mirrors. Let us assume that OP's given curve $\gamma:[a,...
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  • 172k
4 votes
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Total internal reflection doesn't occur when it is supposed to

Total internal reflection can occur when light is in an optically more dense medium, about to enter a less dense medium. It could occur going from glass to air, but not the other way around. The ...
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  • 13.4k
4 votes
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Refraction across two interfaces: is it correct to use Snell's law as constraint in an application of Fermat's principle?

$\newcommand{\bl}[1]{\boldsymbol{#1}} \newcommand{\e}{\bl=} \newcommand{\p}{\bl+} \newcommand{\m}{\bl-} \newcommand{\gr}{\bl>} \newcommand{\les}{\bl<} \newcommand{\greq}{\bl\ge} \newcommand{\...
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