All Questions
5,196 questions
-2
votes
0
answers
71
views
Photons are massless then how do they exist? [duplicate]
If something exists, then it surely has some mass. If photons are massless then they simply should not exist. But they not only exist but have momentum(p) also despite the fact that p=mv and if m=0 ...
0
votes
0
answers
26
views
What makes the polarisation and driving electric field be in phase with each other?
I Don't quite understand why at low frequencies (when the frequency is far from resonance) polarisation is in phase with the driving electric field.
I was thinking the reason could be that, once close ...
- 13
1
vote
0
answers
61
views
Can light exist in 4 spatial dimensions? [duplicate]
Light is electromagnetic radiation, according to what I have learned so far essentially a changing magnetic field inducing an electric field which induces a magnetic field and so on.
The equations for ...
- 19
1
vote
1
answer
64
views
1 watt of power defines as? [closed]
Imagine you have a light bulb of 1 watt power. Then, is 1 watt defined as
•1 joule of electric energy transformed to 1 joule of light energy in 1 sec?
•what exactly is meant by 'consumption' of energy ...
- 23
-2
votes
0
answers
51
views
Color Isolation from Spectrum without Medium [closed]
Would it be significant if a specific color could be isolated from the spectrum without the use of a prism or filter? I wanted to see if I could do this as my current understanding is that it can’t be ...
- 1
1
vote
1
answer
52
views
What causes shadows to be more saturated than the local color of the object?
I am a 2D artist who has recently been studying light and ray tracing to produce more realistic results. I have a general understanding of light now: specular, diffuse, bounce light, diffracted light, ...
- 11
0
votes
0
answers
26
views
Methods to measure the IR intensity light using the Spectrometer
I'm a undergraduate student. Our group of friends plan to measure the IR light source intensity. We have a idea to do this.
In a dark room we place a IR light source in opposite to that we place a ...
0
votes
2
answers
84
views
Light bends in what path? [closed]
I have heard light bends around black holes because they are very massive. That is because the shortest distance there is the displacement along a non planar curved surface where Euclidean Geometry ...
- 167
12
votes
2
answers
1k
views
Is it possible to make a light follow a non-geodesic path?
I just stumbled upon this question.
For massive particles like an electron, it is easy to make them follow a non-geodesic path by applying an external force. In case of the electron, one can put it ...
- 711
2
votes
1
answer
45
views
Light radiation intensity equation [closed]
Is there an equation to convert Light radiation intensity from W/m² to Lux?
Note: The light source is the sun throughout the day (its intensity will vary over the day).
- 21
0
votes
0
answers
41
views
Why is there a colour difference between stars and hot objects since they are both black-body radiators? [duplicate]
I have a question about the color of a black-body radiator that has been baffling me for a few years now, and I haven't been able to find a satisfactory answer. So, we know that a star's color depends ...
1
vote
1
answer
37
views
How could I manually find the field of view of a camera lens at specific focal lengths?
I'm trying to manually find the fov of my FE 24-70mm F4 ZA OSS Sony full frame lens. I know I can find it on the internet, but I want to do a physics/mathematical investigation myself.
I have an idea ...
- 11
6
votes
4
answers
1k
views
Why do telescopes converge light instead of diverge?
I am an astronomy hobbyist and have a 6" Newtonian at my home. While I was collimating my telescope it hit me that why is there a concave mirror at the back instead of a convex mirror.
Why do ...
- 125
1
vote
1
answer
109
views
Did I see the green flash, twice?
I was at the beach today at Costa Ballena in Spain. I was hunkered down to take a photo of the waves and the setting sun. Just as the last part of the sun was about to go below the horizon, I thought ...
- 268
0
votes
2
answers
78
views
Why aren't brightness and loudness represented as spectra? [closed]
I'm curious why brightness (light intensity) and loudness (sound intensity) aren't usually described using a spectrum, which typically shows frequency ranges. Are these quantities measured differently ...
0
votes
2
answers
61
views
What is the direction of the magnetic field of light?
So apparently light is a type of electromagnetic radiation. This implies that it has a magnetic field, which must have a north pole and a south pole. However, we only ever see light propagate one way.
...
- 202
0
votes
0
answers
13
views
How did the first CRT monitors with Beam Penetration create a full set of colors?
Was reading about early CRT methods and came across the idea of Beam penetration, which from what I can tell was the first method of using these devices to make color images: two layers of phosphors ...
- 215
1
vote
2
answers
94
views
Why does from blue to red light (after crossing a prism) the heating effect on interaction material increase?
I was reading this paper for Near Infrared discovery The history of near infrared spectroscopic
analysis:
In his experiment Herschel projected a rainbow on to a bench by the aid of a prism then he ...
1
vote
1
answer
60
views
How to identify if a transparent material is made of glass or plastic from an image alone?
Without using any spectroscopy instruments, how to identify if a transparent material is made of glass or plastic (taking the below image as example)?
Background: I've noticed that the optical ...
- 193
1
vote
0
answers
30
views
Transmission holograms
I would like to realize a transmission hologram for a college project. One of the requirements is to measure something with your own project. So I was thinking about measuring the diffraction index of ...
- 11
0
votes
2
answers
96
views
Why does the critical angle decrease as the frequency of the light wave increases?
In my optics class a problem involved calculating the critical angle for a violet ray vs. a red ray (for total internal reflection), but I'm still confused on how the problem was approached. Could ...
-1
votes
1
answer
149
views
Is the grass greener on the other side? [closed]
Is it? I suspect that with different angles and such (but ignoring the basic structure of grass; resulting in you seeing mostly brown earth if you look straight down on grass) this might perhaps be ...
- 6,817
0
votes
1
answer
88
views
Doppler effect in the case of a moving hydrogen atom
An electron in a hydrogen atom moving at speed $v \ll c$ goes from a state $m$ to $n$, emitting a photon of frequency of $\nu$. In a different experiment, the hydrogen atom is kept at rest and the ...
1
vote
0
answers
32
views
Is there any dielectric material whose dielectric constant varies with applied time varying electric or magnetic field?
I want to achieve UWB communication over light in free space. Naturally, frequency modulation of light comes to mind. Can we do that? How?
My mind says yes. But has anybody tried this?
Is Lithium ...
0
votes
0
answers
40
views
How does light intencity work on a sphere?
I was working on a problem where earth was a blackbody and the sun was shining 1400W/m^2 on the earth. The details of the problem don’t matter but i made the mistake of calculating the power for the ...
-1
votes
2
answers
55
views
Where are the pure colors on CIE diagram? [closed]
Where are the pure colors on CIE diagram?
I think that they are only along the curved edge.
Are the colors in the 'straight line of purples' also considered as pure colors?
Are pure colors only along ...
-1
votes
1
answer
81
views
Can every color between red and green be made using monochromatic light? [duplicate]
Is it true that every color between red and green, can be made using monochromatic light. I think is should be true according to the visible spectrum. I may only need to increase or decrease the ...
-3
votes
2
answers
158
views
Why can colours like RGB $(168, 151, 80)$ be seen by humans?
Is it true that we can only see colors that lie in the visible spectrum? If yes, then why can colors like RGB $(168, 151, 80)$ be seen by humans?
Let us suppose that we are at the extremely red part ...
- 111
27
votes
3
answers
3k
views
Why are the northern lights so much less visible to the naked eye than to smartphone cameras?
The northern lights have been visible where I live recently, but I've found them to be practically impossible to see with the naked eye. Phone cameras, however, show them quite brilliantly. How is ...
- 1,289
0
votes
1
answer
56
views
Deflection of light in linearised gravity
In Sean Carroll’s book, section 7.3, he uses the linearised metric to find the deflection of light around a mass $M$. But a mass $M$ has no energy density around it, so $T_{uv}$ is zero everywhere ...
- 83
1
vote
1
answer
72
views
The Path of Light over an Infinite Plane
An infinite plane with a finite thickness creates a uniform gravitational field, and the math shows that $g=2 \pi G \sigma h$ ($G$ is gravitational constant, $\sigma$ is plane density, $h$ is ...
- 11
0
votes
1
answer
62
views
Was the early universe violet?
If the early universe was packed so densely that it was opaque to light, and did not become transparent until there was enough space for the smaller wavelengths of light to penetrate, then would the ...
- 335
2
votes
1
answer
48
views
An object's colour and its relation to light
I know that an object (say, a block of red colour) appears red because white light from the light bulb or sun shines on it, and the block absorbs all the other wavelengths of light except that ...
- 29
1
vote
1
answer
31
views
Refraction/Dispersion through prism
CASE 1: WHEN TWO IDENTICAL PRISMS ARE JOINED END TO END.
The light ray disperses at the interface of the first prism and then at the interface of the second prism the different components converge so ...
2
votes
3
answers
44
views
Separate dust particles by colour by light
I have a stream of dust with coloured particles. I want to sort those particles by color. We are wondering if it is possible to let it flow by an intens light in a specific color and then extract the ...
- 21
2
votes
1
answer
50
views
A diffraction pattern without central maxima?
In some smartphone charger there exists a bulb (LED) most probably which emits light when charger is plugged in. I have noticed that light coming from that bulb causing diffraction pattern on the wall....
5
votes
2
answers
686
views
Is the light reflected from an object the same as the incident light, or does the object emit a new beam?
When light reflects off an object, is the reflected beam composed of the same photons as the incident light, or does the object absorb the incoming light and then emit a new beam of light that is ...
- 177
0
votes
1
answer
36
views
Clarifying Magnification Values in Photography
Question:
What is the range of magnification produced by a camera lens?
Given the options:
(a) more than $-1$
(b) more than $+1$
(c) less than $-1$
(d) less than $+1$
Context:
I’m trying to ...
- 11
1
vote
2
answers
64
views
Does green transparent glass reflect green light?
I have learnt that green transparent glass only allow green light to pass through, but if that's the case why do green transparent glass appeared green in our eyes when it reflected other light and ...
- 15
0
votes
1
answer
33
views
Evolution of isotropic light in a closed empty room with fully reflective walls
I ponder the following hypothetical scenario:
There is a closed empty room, square in shape (if in 2D space, otherwise cubic if in 3D space), whose walls are fully reflective (in the true hypothetical ...
22
votes
4
answers
6k
views
Why are no metals green or blue?
Copper is orange; gold is yellow; silver, platinum and lead are white (chromatically speaking).
Why are there no metals that are blue or green?
Why do the colours of cold metals follow, more or less, ...
- 329
0
votes
0
answers
25
views
Determining the focal shift using ABCD or in other words ray transfer matrix
Determining the focal length after light passes through a lens is straightforward when the focus is in air, but how should we approach calculating the focal length when the light passes through a ...
1
vote
2
answers
100
views
Won't the violet color of rainbow be mixed with some IBGYOR?
What I have understood is that in rainbow the red is the outermost side because it can come out of waterdrop at 42.4 degree and blue is in the innermost side of the rainbow because it comes out at <...
0
votes
2
answers
40
views
Creating pure monochromes by separating constituent waves
Since we cannot create a pure monochromatic wave, consider a white light wave and let it pass through a prism. Are the colored waves produced by this non-monochromatic as well? If yes, then can't we ...
-1
votes
1
answer
57
views
Why light have gravitational lensing? [closed]
I was reading about light in a book there it was there that light is not a physical quantity, light has no mass as photons are more and more smaller then atoms. Then how does gravity affect the path ...
0
votes
1
answer
88
views
Why does Sun appear white at noon?
I have found several source citing the reason for the white apperance of sun is due to less scattering of light before sunlight reaches an observer on the Earth (as it is relatively closer to us at ...
- 11
-5
votes
2
answers
88
views
If light can't have relative speed, does it get left behind the earth imperceptibly? [closed]
I was just thinking about how if a planet is moving very quickly through space, everything we "throw" from it with mass would leave with a momentum from Earth, like a ball dropped in moving ...
- 1
-1
votes
1
answer
76
views
How was the speed of colored light measured in a vacuum? [closed]
Light is affected by the change in the speed of the source as the frequency of light changes. This is called the Doppler effect, where the red shift can be observed in galaxies moving away from us.
...
-2
votes
2
answers
129
views
Why is a black hole black, according to theory (and observation, and ignoring QM & Hawking radiation)? [duplicate]
I had already edited this question in response to the criticisms of those who closed its first version, as described in my comment below following the first group of others' comments. Perhaps I ...
- 141
0
votes
0
answers
30
views
Eternal Acceleration [duplicate]
I'm a physics graduate, so I have a solid understanding of special but not much knowledge of general relativity. I tried a thought experiment the other day involving a spacecraft accelerating ...
