# All Questions

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1answer
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### Under water light reflection of air in a cup vs water in a cup

The last time I was on vacation I was drinking on the swimming pool, and after I was finished with the drinks I started playing with the 2 plastic cups I had, and noticed that the air produces a ...
2answers
66 views

### Snell's law and Fermat's principle

I have read this sentence on a book about the Snell's law of refraction, referring on a ray that passes from air ($n_1=1$) to glass ($n_2=1.55$): "Snell's equation can be derived from Fermat's ...
1answer
51 views

### Focal Power of a Plane Interface

We know that when converging beam of rays are more converging after passing through an instrument, then we say it is of positive focal power. If angle of convergence doesn't change it is of zero focal ...
1answer
55 views

### Bending a Laser Beam [closed]

We can bend a Laser beam by varying the refraction coefficient of the air. We can bend a Laser beam by dispersing into the air small particles that have the same effect on the Laser Beam and small ...
2answers
199 views

### Is there a formula to calculate the deviated angle of a ray passing through a prism?

I'm assuming the angle of incidence to be the number of degrees from a perpendicular line on the side of a prism the ray starts passing through... I'm trying to figure out the angle the ray would be ...
1answer
53 views

### Curved Light stream?

I was wondering, a while ago, i asked if there is a way to bend light someway, which I got the answer is index of refraction. Which is when light passes through a material it refracts to a certain ...
2answers
89 views

### Why does violet light bend the most? [duplicate]

When white light passes through a prism, refraction occurs and it splits into its seven constituent colours. If the spectrum is obtained on a screen violet light appears much more bent than red light. ...
2answers
32 views

### Angles of Refraction,Internal reflection and incidence

First ill ask my question in brief and then ill elaborate it below... Theoretically is it that internal reflection occurs within a solid sphere(which is considered to be the denser medium) if and ...
1answer
221 views

### Determining the refractive index of a glass slab using a travelling microscope

In this practical video of finding the refractive index, the reading is being taken by placing the travelling microscope perpendicular to the slab. But I've learned in another video(Frame Shot) if you ...
1answer
21 views

### Calculated focus of an asymmetric bi-convex lens

So I've been working on modeling an optical system using ray tracing. I've finally gotten to the point where I am testing things however I've come across something I'm not entirely sure of. I'm ...
4answers
2k views

### Reverse of diffraction

Can we arrange a practical in such a way that the dark and bright bands in diffraction grating be allowed to pass through the same slit to get the original light (i.e the incident light before ...
1answer
80 views

### Do photons “bounce off” of electrons?

I’ve been reading a book, and in one part the author explains how electrons only absorb the wavelengths of light that can take them to an excited state, i.e. that can take the electrons to a higher ...
3answers
4k views

### Why doesn’t a normal window produce an apparent rainbow?

When light refracts in a prism it creates a rainbow. My question is, why don’t all windows or transparent objects create this dispersion, i.e. why is the refractive index dependent on frequency in a ...
1answer
50 views

### Why does the intensity of the scattered light vary when a monochromatic laser is shined into a transparent object?

When a laser is shined into a glass ball such as this video (link) or a bottle of water (link) the light is refracted through the whole transparent body. However, the intensity of the light scattered ...
2answers
6k views

### Why don't light beams refract when they hit a curved surface [closed]

I saw a diagram that showed a light beam hitting a curved glass block (half circle) and nothing happened until it hit the flat surface, in which it refracted. Why doesn't it also refract when it hit ...
2answers
108 views

### Why does a prism refract light into a rainbow? [duplicate]

Why does a prism refract light such that the different frequencies of light “spread out”? The same goes for rainbows, why do the raindrops “spread out” the different frequencies of light?
1answer
52 views

### Why light travels through shortest path during refraction?

I know in order to compensate with change in speed but how does Light actually know which path is less dense or more dense?
4answers
75 views

### Why does frequency remain unchanged in light refraction but wavelength doesn't? [duplicate]

Since the frequency of an electromagnetic wave does not change during refraction but the velocity changes, the wavelength must therefore change. But why doesn't the frequency change in the first place?...
2answers
32 views

### Radio Waves / Light: Atmospheric Refraction

The following image differentiates between a visual horizon and a radar horizon. Sidenote: I'm not too familiar with primary surveillance radar technology, but this image refers to secondary ...
3answers
4k views

### Can air make shadows?

I have read about schlieren photography which uses the ability of non-uniform air to create shadows. Is it really possible that air makes shadows?
1answer
31 views

### Refractive index and optical fibre question

This is an A level AQA question: A signal is to be transmitted along an optical fibre of length 1200m. The signal consists of square pulses of white light and this is to be transmitted along the ...
4answers
2k views

### Light propagating through a sound wave

We know that the speed of light depends on the density of the medium it is travelling through. It travels faster through less dense media and slower through more dense media. When we produce sound, a ...
1answer
43 views

### Speed of light dependent on source velocity in other medium [duplicate]

Does speed of light depends upon the velocity of source in a medium (like water) other than space? if yes, does the speed gets added up when the light source moves in direction of light?
0answers
58 views

### How does a concave lens form a virtual image?

If rays of light are diverged upon exiting a concave lens, then they have no focal point. The rays completely spread out in random directions. Like diffuse reflection(which does not form an image) So ...
2answers
289 views

### Condition for constructive interference of light question

The question was asking me to find an expression for the constructive interference between light which follows the paths $PQ$ and $PRS$, once the light has reached the air outside of the two glass ...
0answers
24 views

### Predictions followed from Fermat's Principle, according to Feynman

In his book Lectures on Physics, Feynman mentions two predictions followed from Fermat's Principle (chapter 26-4). 1) Given three media air (1), water (2) and glass (3) with indices measured against ...
2answers
60 views

### Refraction of light with destructive interference

The wavelength of light determines it's refraction in a prism. But, what if two beams of light destructively interfere as they pass through a small prism, so there is no apparent wave or wavelength ...
4answers
12k views

### Relation between intensity of light and refractive index

The intensity of light (as calculated from time average of the poynting vector) is given by $I = (1/2) \epsilon v E_0^2$. Here the intensity is dependent on the velocity of light in the medium. The ...
0answers
10 views

### Velocity vectors during the propagation of photon in elastic scattering question [duplicate]

I have been trouble with the concept of energy of the photon during propagation in random scattered or random continuum medias. E = hf, where E is the energy of the photon in Joules; h is Planck's ...
3answers
123 views

### How is energy conserved during simultaneous refraction and reflection of light?

My question is regarding the partial reflection and refraction of light when incident on a refracting surface. Here, the energy of Incident Ray is E=hv of Reflected Ray is E=hv and that of Refracted ...
1answer
62 views

### Speed of electromagnetic wave [closed]

On dispersion , speed of wave is inversely proportional to its wavelength . Therefore, gamma has max speed. But then in visible light , violet has least wavelength still it has least speed in visible ...
0answers
41 views

### What is happening to a wave at a media boundary?

Say we have a light wave going from air to plastic, refractive indexes 1 and 1.5 respectively. What exactly is happening to the properties of the wave and why? Taking wavespeed as v, frequency as f, ...
2answers
105 views

### What does it mean to say that glass has refractive index 1.5?

The refractive index of a material depends on the wavelength of the light incident upon it which is why dispersion happens. When we say that glass has refractive index 1.5 which wavelength do we have ...
1answer
202 views

### Geometric optics multiple lenses

I am confused on how light rays behaved in this figure, specifically when it passed through the diverging lens. Why would the light rays converge when it passed through the diverging lens, when it ...
2answers
106 views

### light travels the fastest path of two points, how do you determine those two points?

so in this diagram from Richard Feynman's book: QED Strange Theory of Light and Mater the light takes the fastest path from S to P and the lens makes it so that there are many fastest paths that go ...
2answers
57 views

### Is snow falling too fast or too reflective to produce rainbow?

Imagine millions of water molecules suspending in the air starts to turn into snow, I like to know the exact reason why we cannot have snow bow, is it due to the speed of each snow falling very fast ...
1answer
293 views

### Why does light take the path taking the least time?

I know this question has been asked many time but my question is bit different here. What i mean by the above question is that I recently got to learn that light actually does not exclusively take the ...
1answer
384 views

### Comparison of refractive index of red and blue coloured light

My text book gives $v/c$=refractive index as 1 of the formulas to calculate. Now, \begin{eqnarray} v({\rm red}) &>& v({\rm violet}) ~~~\mbox{and let glass be the medium} \\ \frac{v({\...
1answer
2k views

### Why does the sky look darker blue directly above me, but get lighter in the distant sky?

it seems that the sky looks a bit darker right above me, but if I look into the distance, I see a paler blue.
2answers
77 views

### Property of light in different media?

Shouldn't keeping a colored frame in front a flash light ( white light ) change its wavelength or frequency?But I have also learned that light doesn't change its frequency when going from one medium ...
1answer
65 views

### What causes these diamonds in water droplets on a screen?

It was raining yesterday and the screen of my iPad ended up covered in varying sized water droplets. As you can see, the smallest water droplets look transparent, and then as the size increases the ...
1answer
141 views

### Why is the thin prism always in the position of minimum deviation? [closed]

Our textbook says that a thin prism (a prism of angle less than 10°) is always in the position of minimum deviation, but doesn't provide any explanation as to why that it is. What would happen if I ...
2answers
86 views

### image formation by lenses

Why is the image formed by an object as described in the picture can be derived only from these three ray of lights?Every point on the object has multiple ray of lights going in every direction, how ...
2answers
872 views

### Does Snell's law still apply after total internal reflection has occurred?

Snell's law states that: \begin{align} n_1\sin\theta_1 &= n_2\sin\theta_2\, ,\\ \sin\theta_1 &= \frac{n_2}{n_1}\sin\theta_2\, ,\\ \sin\theta_1&\propto \sin\theta_2\, . \end{align} The ...
2answers
436 views

### Is it possible to calculate the distance to a rainbow by using the parallax method?

A colleague of mine (a physicist) recently claimed that it is possible to calculate the distance to a rainbow by applying the parallax method and that the result would be ~150 million kilometers, the ...
5answers
593 views

### Is there a medium less dense than vacuum, in which light can travel faster than $c$? [closed]

Is there a medium less dense than vacuum, in which light can travel faster than $c$? If not, can we make it?
3answers
302 views

### Why do rainbows always appear to be far away from us?

We know that the single rainbow we see is actually a continuous cone of rainbow. If so, why don't we see that cone instead of a single, far-away rainbow?
2answers
61 views

### Why don't images bend when looking through window glass like they do when looking through water?

From this section on wikipedia, the phenomenon of an image appearing warped or slightly displaced when looking through water is due to its index of refraction (1.33) deviating from that of air (~1). ...
6answers
14k views

### Does light loses its energy when it passes through denser medium?

I know it does not because it emerges out of denser medium at 300,000 KM per second, but according to $E=mc^2$ and given that speed of light decreases inside denser medium with refractive index ...
2answers
84 views

### Why does purple appear in a rainbow?

It is said that people and digital cameras have color sense only for red, green and blue. So when we see violet/purple in a rainbow, whether with our eyes or in a photo, we should be seeing a color ...