Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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13
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4answers
1k views

Looking for the actual reason of refraction explained precisely without analogies

I'm a high school teacher trying to teach my students (15year olds) about refraction. I've seen a lot of good analogies to explain why the light changes direction, like the marching band analogy, that ...
5
votes
2answers
88 views

Redshifting of light from a moving light source

We know that the expansion of space causes redshifting of light. I even read somewhere that the Doppler effect also happens in light. So imagine I switch on the headlights of my car in front of a ...
0
votes
1answer
60 views

Does firing electrons at an object change its colour?

If one had an electron gun capable of firing electrons with a specific energy at an object, can it change its colour? I think it is possible because the emission spectrum of the material would ...
1
vote
1answer
147 views

photon polarization, uncertainty in Energy

A beam of red light is sent along the $z$ axis through a polaroid filter that passes only $x$ polarized light. The beam is initially polarized at $30$°, and the total energy is $10$ Joules. Estimate ...
2
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3answers
168 views

Electromagnetic Waves

We all know that light is an electro magnetic wave. but is electricity a EM wave? If it is then why light does not requires a medium to travel and why on the other side electricity needs a conductor ( ...
1
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3answers
210 views

Does the velocity of a light source influence the light

I have only just finished High school physics so my understanding is still fairly simple but I'm having trouble with this question. Imagine you are in space traveling at a relativistic speed with a ...
-1
votes
1answer
63 views

Determining a person's sight from his speech [closed]

Suppose we meet a person wearing glasses.Can we determine whether the person is short-sighted or long-sighted? However,due to courtesy,we are not allowed to ask him to try the glasses and in general ...
1
vote
1answer
302 views

Visible light through a single-mode optical fiber?

If I understand things correctly, the optical fibers used for (long-range) data transmissions are generally single-mode fibers, transmitting light in the 1300-1500 nm spectrum. Now, could such a ...
1
vote
3answers
143 views

How far does a Photon's field Extend?

I read the related answer to whether photons have size, and the answer seemed to be it depends. If a Photon, or a rather an E&M wave has a magnetic and electric field, should things be able to ...
0
votes
1answer
37 views

Resampling spectral data?

I want to use the CIE CMFs (Color Matching Functions) provided here: http://www.cvrl.org/cmfs.htm With data from my spectrometer in 10 nm increments. However, the CMFs are only provided at 5 nm ...
0
votes
1answer
130 views

Implications of Formula for Stellar Aberration

I am studying relativity and was working on deriving stellar aberration using relativity. My derivation is as follows: Suppose that the observer is traveling at a velocity $v$ in the $x$-direction. ...
3
votes
2answers
263 views

Is the frequency/wavelength of light modified when multiple light sources are combined?

Let's say I light a wall with two spotlights: One red and one green one. Where they overlap, I'll see a yellow area at the wall. My question is, whether this is caused by an modification of the ...
2
votes
2answers
108 views

Are there any materials that change the electromagnetic wavelength of visible light?

What i mean is for example exclusively red light comes in but gets reflected or refracted as blue or xray wavelength or whatever. Does this happen at all?
2
votes
2answers
126 views

Einstein's Postulates: Simultaneity

Okay, I still don't get the solution (which I will lay out) to the following problem: Suppose that A', B', and C' are at rest in frame S', which moves with respect to S at speed v in the positive ...
-1
votes
1answer
69 views

Is Tube light polychromatic?

Is tube light/fluorescent lamp monochromatic or polychromatic? Please justify.
2
votes
2answers
144 views

Can we have light through out the house with out light being switched on for all the time?

Optical fibres are used to transmit light from one place to the other along curved path in a more effective manner. The optical fibres consist of thousands of strands of a very fine quality glass or ...
0
votes
1answer
91 views

What physical phenomena underly the shape of this graph of diurnal UV index?

When I dig up a graphs of UV index versus time-of-day, most graphs are characteristically shaped like one of the plots shown here: That graph is from this site. What physical phenomena underly ...
0
votes
4answers
276 views

Can we create invisible things?

We are able to see this beautiful world because of light. When light gets reflected from the object, the reflected light enters our eye retina and thus we are able see that particular object from ...
2
votes
2answers
192 views

Can we observe diffraction even if the slit size is tending to zero?

According to Huygens principle, if we consider any point of the primary wave fronts, each point is the source of secondary disturbance. If the point size we consider tends to zero, the number of ...
0
votes
0answers
56 views

Spatial light modulation for mode multiplexing, how does it work?

If a laser light becomes spatial phase modulated (by phase only spatial light modulator) what happens to the intensity distribution and frequency spectrum of the laser light ? I know that this ...
3
votes
2answers
158 views

What is the energy distribution of light if it has an infinite length?

What is the energy distribution of light if it has an infinite length? I have read in one of the answers here on phys.SE that light has actually an infinite length. But then what is the energy ...
3
votes
2answers
46 views

How should I interpret an article about light being slowed and compressed?

I've found an article describing a method that allowed the light to be "slowed and compressed"... That sounds really strange, which made me google a lot and find this PDF document. However for me, ...
1
vote
4answers
89 views

Coherence effect on collecting sun light by mirrors

There are systems that collect sun light in one spot. I wonder, why does it accumulate additively, without destructive interference?
3
votes
2answers
99 views

Why does the colour wheel wrap around?

Red colour bares 430-480THz and Violet bares 670-750THz according to Wikipedia. What frequencies are the colours between red and violet? Will they be higher than red? or lower than violet? What ...
2
votes
2answers
58 views

Frequency of Light Near a Massive Object

We know that near a massive object, light's wavelength and frequency changes, but its speed remains same. I'd like to know how it is possible for frequency to change, unless we change the light ...
-1
votes
3answers
190 views

According to relativity, can a statement be true and false in same time?

Say I write following statement on a paper: It's year 2014 at earth. Then I give it to my friend. My friend then starts to leave me and earth to outside with velocity of light. Einstein says the ...
0
votes
2answers
290 views

Is it possible to project an image onto water? [closed]

Is there a way to create an image/projection in the water? Or form the water to project an image, little dot/pixel? Use some type of frequency to modulate the little dot in the fluid?
1
vote
0answers
47 views

How does a liquid crystal on Silicon affect the phase of incident light?

When a polarized light beam is directed to a phase-only LCoS system how is the phase modulated ? What is the physical effect behind ? Does voltage modulation has an impact on birefringence ?
2
votes
2answers
627 views

Relationship between measures of light (candela and lux)

I am trying to understand the relationship between two measures of light: lux and candela. It is probably easy for those with longer experience, but here it goes: I have learnt (here for instance) ...
7
votes
4answers
326 views

What {R,G,B} values would represent a 445nm monochrome lightsource color on a computer monitor?

Is it possible to answer my question definitely (assuming the monitor is perfect)? What would be the formula for calculating RGB values for a visible monochrome light with given wavelength?
0
votes
3answers
187 views

Refraction through prism

We know that the light gets refracted when it enter a medium low/high refractive index. But why light is not refracted when it comes out from the vertex of a prism.
2
votes
3answers
254 views

During reflection does the emitted photon have same properties?

When light (photon) is reflected the the original photon is absorbed by an electron and then emitted again. Does this "new" photon have the same wavelength, frequency etc. as the original?
4
votes
3answers
184 views

Why does the point of intersection of two shadows look brighter?

When I sit in my garden during the day I always keep looking at the two intersecting shadows of two rods. It looks something like this: What I find weird about it is that at the point of ...
91
votes
6answers
8k views

Very strange shadow phenomenon

I was laying on my bed, reading a book when the sun shone through the windows on my left. I happened to look at the wall on my right and noticed this very strange effect. The shadow of my elbow, when ...
1
vote
1answer
488 views

What causes refraction of visible light? [duplicate]

Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the ...
0
votes
1answer
154 views

Difference between mirror reflected light rays and rays of a screen

What is the difference between the light rays reflected from a mirror and rays directly emmited from a screen if the screen shows the same image as the mirror would.
1
vote
2answers
507 views

Why are two independent sources incoherent?

Coherent sources are produced from a single parent source. But, why are two independent sources always incoherent? Two sources can produce light of the same frequency. Then, I guess the problem is ...
0
votes
0answers
32 views

Axis of reflection in a mirror [duplicate]

When I look at my reflection in a planar mirror, the image I see is reflected about a vertical axis. Why is it this axis and not the horizontal axis?
0
votes
3answers
65 views

Wall visible after light source removed

Let's say you have a lamp pointed at a wall, in a dark room with no other light source, if you turned off that lamp Would the wall still be visible for any amount of time?
0
votes
0answers
48 views

What creates black streams in fountain-type fireworks?

For the New Year celebration of 2014, my nephews set off a series of fountain-type fireworks (as shown below). When one looks carefully into the shower of light, one notices that a fair number of ...
1
vote
2answers
563 views

Why is the blue color of sky darker in high altitude regions?

I read that as the air density is lower at high altitudes, the scattering is less, hence the darker blue but then other colors are scattering lesser than blue, why don't we see a darker shade of the ...
1
vote
1answer
93 views

Can Massless Particles Have Dimensions? [duplicate]

We have been taught that anything occupying space/volume has mass. Light has both a particle nature-photon and wave nature. Since It has an momentum of h/λ, energy of hc/λ. Since a photon carries ...
0
votes
1answer
37 views

Diffraction from interatomic spacing

In diffraction from a single slit, we learn that the angular width of the central maxima, is given by $2\sin^{-1}\frac \lambda d$. For $d\approx \lambda$, the incoming wavefront should be spread to ...
4
votes
4answers
314 views

Why do the passing objects' shadows run in the direction of the moving train?

While travelling in the train on the sunset, I have noticed the strange phenomenon. The shadows of the lonely trees and lampposts, that stay along the railroad, are moving on the wall in the same ...
0
votes
0answers
16 views

What is the amount of EM energy from the sun reaching the earth as a function of wavelength?

The question stems from a desire to know if more light from the sun in the infrared wavelengths has more energy than light at say yellow or violet wavelengths - at the Earth's surface. I'm guessing a ...
1
vote
1answer
149 views

Why can't we see things swallowed by black holes?

Apologies in advance, I'm a layman with only a school-level education in physics. If an object approaching the event horizon of a black hole has its light cone progressively bent towards the black ...
0
votes
1answer
78 views

What is the intrinsic colour of the star? [closed]

Hey I have this question and I am wrestling with it all day and I am completely lost. The V magnitude of a star is 15.1, B-V =1.6, and absolute magnitude Mv= 1.3 The extinction in the direction of ...
3
votes
1answer
107 views

Polarisation of light is a wave concept or applicable to photons as well?

I have a very fundamental question. We explain polarisation of light assuming wave nature of light. Is it still valid if we assume light as photons? Or in other words, polarisation is a wave concept ...
6
votes
7answers
470 views

Is the sun's solar radiance spectrum matching up with water's absorption spectrum just coincidence?

People frequently point out that water has a pretty narrow range in which it isn't very absorbing of light, reaching a minimum at a wavelength of about 500nm: And that our eyes have made good use ...
0
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1answer
87 views

Young's DS experiment and most light sources

The reason why two independent bulbs cannot be used to create the young's two slit interference pattern is that the phase difference between those two sources varies very rapidly and therefore, the ...