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.
1
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2answers
111 views
Do photons actually generate a slight kinetic force?
My question is even though photons have no (rest) mass, do they emit a external force due to EM radiation causing electrons to be excited and jump to higher energy shells which electrons have mass ...
0
votes
2answers
69 views
Observing visible light itself by our eyes
We know that for any object to be seen by a human eye, the light from any source must be reflected from that object so that it reaches our eye and we can detect it.....but how do we see light itself? ...
14
votes
6answers
1k views
Why cannot we store light in form of light?
We can store cold (ice),heat (i.e. hot water bag) and electrical charge (batteries). We can even "store" a magnetic field in a magnete. We can convert light into energy and then, if we want, back to ...
3
votes
1answer
319 views
Gravitational Redshift around a Schwarzschild Black Hole
Let's say that I'm hovering in a rocket at constant spatial coordinates outside a Schwarzschild black hole.
I drop a bulb into the black hole, and it emits some light at a distance of $r_e$ from the ...
0
votes
1answer
118 views
The nature of light
I'm not sure if this has been answered before, but I figured this would be the right forum to find out. I'm not by any means an expert in physics, just someone who's interested in understanding more ...
-1
votes
1answer
122 views
How do photons experience time? [duplicate]
I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below.
1)So I want to know how time is perceived from the point of view of the photon?
2)Since ...
0
votes
2answers
258 views
EM waves: How do they travel for billions of km without damping
If a star is 1 billion light years away, it means that the light we see from the star is emmitted billions of years ago.
How does this light not undergo a frequency change or get damped inspite of ...
2
votes
1answer
62 views
A question about how light hits a surface
my question is about how photons travel from a light source and hit an object.
When you look at an object being hit by light the whole surface becomes brighter.
What i'm trying to understand is why ...
0
votes
2answers
259 views
Young's Double Slit experiment question
Q-A beam of light consisting of two wavelenghts 600 nm and 450 nm is used to obtain interference in Young's Double Slit experiment (YDSE). Find the least distance from the central maximum where the ...
1
vote
0answers
11 views
Speed of Light in a Medium [duplicate]
For light travelling in a medium with refractive index greater than one:
The "average" speed of light is slower than the speed of light in a vacuum. As far as I know, the instantaneous speed of light ...
1
vote
0answers
13 views
Is it possible to calculate chromacity coordinates using absorbance values?
I have absorbance values for blood plasma. Absorbance was measured in range of 380 – 600 nm every 5 nm ending up with absorbance values for 45 wave lengths. I was browsing through literature, and I ...
0
votes
1answer
83 views
What is the momentum of these emitted photons?
5 x 10^7 kg of radioactive material emits energy in the form of photons of red light (700 nm). (Note: photons have no mass.)
What is the momentum of each photon?
...
8
votes
3answers
907 views
Is it possible to reproduce Double-slit experiment by myself at home?
I want to reproduce this experiment by myself. What I need for this. What parameters of slits and laser/another light source it needs? Is it possible to make DIY-detector?
0
votes
2answers
60 views
Can a stream of photons to be an environment for carrying light?
As the air molecules are environment for carrying sound waves, could stream of photons be environment for carrying electromagnetic waves? What contradictions cause this assumption in the existing ...
-1
votes
1answer
203 views
Frequency Of Light
I am confused on few topics...
What is meant by "Frequency of Light"? Does the Photon(s) vibrate, that is known as its frequency? If the Photons vibrate, then they have a specific frequency, then ...
0
votes
0answers
17 views
How wide is a pre- and post-selected light beam?
To pre-select the beam, we will require that it pass through two holes A and B.
This will allow us to select both a diameter and a divergence angle.
To post-select the beam, we will require that it ...
4
votes
0answers
125 views
How fat is Feynman’s photon?
According to my calculations, it is a lot skinnier than Airy’s photon, but still a whole lot fatter than a straight line.
So, how does a photon get from point A to Point B?
The ray optics ...
5
votes
1answer
161 views
3D movie glasses making white light look red and blue
While waiting for a 3D movie to start, I was playing with the glasses they give you. I understand each lens has different polarized filters, so the left and right superimposed images on the screen go ...
-2
votes
2answers
114 views
If we are travelling with the speed of light, can we see what's behind us? [closed]
If we are travelling with the speed of light, can we see whats behind us(like if we are moving away from earth can we able see the earth)? And how we see the things that we are approaching with speed ...
3
votes
1answer
82 views
How would I perceive a purple ball when traveling at relativistic speeds
I have a 'thought experiment' which I'd like to ask about.
I was thinking what speed I would have to drive towards a crossing to see a red light as a green light - pretty easy, using the doppler ...
2
votes
1answer
84 views
Question on Radiance equation
The radiance equation is
$$
L = \frac{d}{dA} \frac{2(\phi)}{dW cos(\theta)} (watt/srm^2)
$$
where $\phi$ is the flux.
I am thinking, should not be the cosine term on the numerator instead of the ...
-1
votes
1answer
91 views
Are more/other colors posible with other dimensions?
Like these impossible colors (yellow/blue and green/red) or these imaginary colors, for example saturated red more intense than pure spectral red can be viewed in ordinary viewing conditions. Can ...
3
votes
1answer
135 views
Was the choice of red/green colors for traffic lights a happy coincidence?
All of us have learned since secondary school that the reason we use red in the traffic lights for "Stop" is because it travels the furthest without dispersion. According to wikipedia which cites ...
0
votes
1answer
55 views
Any suggestions for units conversion? [duplicate]
Possible Duplicate:
Photometer: measured Irradiance L converted to photon rate
I am conducting a experiment where stimulus output of $470\ nm$ is measured by a radiometer at $30\ \mu W\ ...
1
vote
1answer
160 views
Photometer: measured Irradiance L converted to photon rate
I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source.
I wish ...
0
votes
1answer
41 views
Regarding “Holes” in bands, and Photons
So from learning Band theory, and PN Junction and such, I've learned that photons are created when "holes" are filled in a band, and this is what can create light (Isn't this how LEDs work?)
Anyways, ...
3
votes
1answer
134 views
Does light induce an electric current in a conductor?
I know that electromagnetic waves induce electric currents in conductors and that's the basis for radio, wi-fi etc.
I also know that light is also an electromagnetic wave. So, can light induce a ...
4
votes
3answers
414 views
Does light change color on its way through a window?
Looking at the refractive index of glass, it's around $1.6$.
Then the speed of light $x$ through light should be given by
$$ 1.6 = \frac{3.0\times10^8}{x}, $$
so $x$ is about ...
0
votes
2answers
113 views
Can I see the light from 10 million km away?
If light is switched ON, only for a second, and the distance between the observer and the light source is 10 million kilometers, can I still see the light spark?
For example, let's assume that the ...
1
vote
1answer
236 views
Resistance of Light Dependent Resistor (LDR)
Is there a mathematical expression relating the resistance of Light Dependent Resistor (LDR) with light intensity?
2
votes
1answer
100 views
Commercial Infrared lights
I purchased an infrared light. It's a 100 W Philips infrared lightbulb. Says it's infrared, but I haven't done any spectrum analysis so I don't know for sure if it's just red or really infrared.
As I ...
2
votes
0answers
54 views
Was Einstein's Cross Predicted by Einstein's Theories? [duplicate]
Possible Duplicate:
How does gravitational lensing account for Einstein’s Cross?
Einstein's Cross is a fascinating phenomena for which I have asked explanation here. However, I'm also ...
3
votes
2answers
174 views
Why do hot objects prefer to emit photons over electrons ? Is there electron-positron annihilation?
Why do hot objects prefer to emit photons over electrons ? Is there electron-positron annihilation ? If so , why ? Im confused by this.
0
votes
1answer
139 views
Confused about fire?
Im confused about fire.
The way I see it :
Heat creates (kinetic) energy in mass and this creates stronger vibrations of atoms.
When those vibrations are strong enough the electrons interact ...
-1
votes
1answer
288 views
Focal length of Convex lens [closed]
A lens forms a real image of $3\ \text{cm}$ high of an object $1\ \text{cm}$ high. If the separation of object and image is $15\ \text{cm}$, find the focal length of the lens.
2
votes
1answer
120 views
Can light be canceled by merging with an inverted wave?
Can light waves be canceled by merging them with their inverted waves? Seems like it would violate conservation of energy but waves are added together when they overlap, right? Where is the flaw in ...
2
votes
1answer
104 views
How would one generate Brownian light? What would it look like?
When light is an equal mix of all visible frequencies, we call it white light.
By analogy, sound that is a mix of all audible frequencies is called white noise.
For sound, there is an additional ...
-1
votes
1answer
79 views
Are the speeds of the different wavelengths of visible light different or varying in a medium such as air?
Are the speeds of the different wavelengths of visible light different or varying in a medium such as air? If so, please inform by how much?
Also, even if the wavelength speeds vary minimally, please ...
6
votes
1answer
227 views
Why both yellow and purple light could be made by a mix of red, green and blue?
We see the mix of red light and green light as yellow light (#FFFF00). The wavelength of yellow light lies between red and green.
But the wavelength of purple light lies outside of red and blue. ...
0
votes
3answers
484 views
Intensity of light
If we have 2 beams of light with equal intensities, but with different frequencies, wouldn't the one with the higher frequency generate more power?
If so, how come the intensity, which is in $W/m^2$, ...
1
vote
4answers
172 views
Is infrared light diffused on walls?
Lamps that produce visible light can light up a whole room because the ceiling and the walls diffuse light. This way, when there is a single lamp in a room, something that is in the shadows is not ...
-1
votes
1answer
184 views
How can you test what color different people perceive? [closed]
If I would show someone a yellow object and ask them, "is this object yellow?"
That person would say "yes".
But I could never know if my perception of the color yellow is the same as that other ...
-1
votes
2answers
71 views
Why photo cannot be captured while facing toward the Sun /
When the Camera is facing toward the Sun and a person is standing to and We're capturing his photo , all we get is a black shadow even when we capture with the flash light or anything.
Why does it ...
2
votes
3answers
811 views
Is there something special in the visible part of electromagnetic spectrum?
I always wondered how much information we get from color. Things we see have different colors; edible products change color when began to spoil so we have a notion what color a fresh product should ...
11
votes
2answers
840 views
Is the “How to break the speed of light” minute physics video wrong?
I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views.
In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
1
vote
1answer
455 views
Why doesn't my pinhole camera work?
We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown :
But when I'm doing this little experiment with an apple, no matter how I change ...
41
votes
10answers
4k views
Is it possible that there is a color our human eye can't see?
Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it.
If there is, is it possible to detect/identify it?
1
vote
3answers
95 views
Redshift of light in dark matter
Following Edwin Hubble, it is widely believed that the universe is expanding, which is based on the red-shift of light from distant objects. Can dark matter cause light to be red-shifted and make it ...
2
votes
2answers
189 views
How does scattering work?
Why is the sky blue?
I was always taught in high school that light with wavelength $\lambda$ acts like a little particle that wiggles up and down through space (in proportion to its magnitude). I was ...
0
votes
0answers
34 views
Need to write a function that computes the UV index
I have found a lot of people talking about how to compute the UV index, but have not found an example that shows the actual equations, so I could adapt them into an algorithm.
Probably the closest ...
