# All Questions

27 questions with no upvoted or accepted answers
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498 views

### 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 ...
71 views

### Why is refractive index equals to speed of light upon phase velocity and not group velocity?

We have been using group velocity for most purposes as its the velocity with which the wave packet travels, they why do we use phase velocity for calculating refractive index.
227 views

### Integrating over Snell's law with a varying index of refraction

I am working on a research practical and I encountered the problem of having to integrate over Snell's law. The exact problem is that I have a varying index of refraction, which is a function of the ...
71 views

### Odd order of colour fringes around cloud

The other day I took this photograph of a thundercloud that moved between myself and the sun. Around the edge of the cloud there were some coloured fringes that I first took to be a variant on a ...
33 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 ...
69 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 ...
61 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 ...
66 views

### what is the refraction index in the upper atmosphere(e.g Theromosphere)?

I've been searching for the refraction index in the upper atmosphere such as Stratosphere and Thermosphere but I can't find it, all that I've seen is all equation without any number that I can use it. ...
96 views

### Is there a way to explain a rainbow in an almost-QM-correct way to a 5 year old child?

My toddler asked me "how does rainbow happen", and I would like to give a pedagogical explanation of the relation of photon frequency, its color, and the way different frequencies are bent in a drop ...
221 views

### Gaussian beam refraction

I'm trying to understand how Gaussian beams interact with matter. Maybe I have a conceptual issue, but is the beam in the image not propagating in the z direction? In that case, I want to understand ...
74 views

### Is it possible to construct a lens which focuses all the light rays from an extended object in one point?

A perfect lens focuses the light rays from an extended object (in a plane at a constant distance from the lens), in the focal plane corresponding to the distance of the object. Now there is an ...
100 views

### What is the phase velocity of light in graphene?

This article states that light can "slow down by a factor of a few hundred" when it strikes graphene. I've read elsewhere that the index of refraction of graphene is about 2.65 + 1.27i. According to ...
50 views

### Rainbows at the surface of calm cold water : mechanism?

Pictures Bigger versions : First | Second On this one we see the other side of the "main" arc and the white surface of water (see below). Observations So I observed these rainbows in a calm river. ...
72 views

### Making sense of sinogram of perspex block in air

I'm confused trying to visualize what happened exactly during this experiment: Setup with a laser and a photo diode on the opposite side. A perspex block (2x2cm) in between. Take 200 measurements ...
24 views

### Refracting an image through 2 prisms

my question might be quite simple for some of you but I don't have any idea what the result of such an experiment would be... If you would take an image emitting light such as a video from a screen ...
95 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 ...
25 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 ...
305 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 ...
42 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, ...
120 views

### What type of mirage is this?

I am very new to the world of mirages and would like some information as to the type of mirage in this picture which I took this morning. It is the cargo ship African Kalmia which passed my location ...
86 views

### Index of refraction for travelling EM wave problem

Let $n_1$ be the index of refraction of the first medium and $n_2$ be the index of the second medium. When $n_2>n_1$, then for an incident angle of $90^{\circ}$ we get a refracted light at a ...
52 views

### What is A2L refractive index polynomial?

I'm working with a photonic modelling software and in the manual I saw that I can specify refractive index of modelled material with following polynomial: n(\lambda)=c_0+c_1/(\lambda-\lambda_0)+c_2/...
206 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 ...
960 views

### Dispersion in a rectangular prism

Why are the colours visible only at the fringes of the light refracted through a rectangular prism?
188 views

### Why we don't observe spherical rainbow?

We have seen or heard of rainBOW and circular rainbow but not any other shape probably due to the shape of water droplets. My question is why can't we see a spherical rainbow?