Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).
The primary properties of visible light are intensity, propagation-direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature, as with all types of electromagnetic radiation (EMR), light is found in experimental conditions to always move at this speed in a vacuum.In physics, the term 'light' sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of electromagnetic radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed. The absorbed energy of the electromagnetic waves is called a photon and represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave instantly collapses to a single location and this location is where the photon "arrives". This is what is called the wave function collapse. This dual wave-like and particle-like nature of light is known as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics.
The main source of light on Earth is the Sun. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight.
Is red shifting of light from distant stars actually caused from them moving away from us, or is this a simplification.
Doesn't this break the rule of light always going the same speed.
Could the light rays be possibly lengthened because when the light left many yrs ago space was smaller, now it...
a. We know metals emit EM radiation upon heating or electric current. I'd like to understand more fundamentally how this phenomenon takes place, on the basis of the basis of band structure, and which electrons are involved ?
b. Classically, charges emit radiation when accelarating or...
What kind of imaging system could be used to see without photons? I ask because I was watching a video and the furthest we can see back is Redshift Z~1090 which is the CMB. We can’t see the universe before the first stars formed or the Big Bang itself. My first guess would be some kind of dark...
In this thread, I set out an analogy illustrating what quantum entanglement is; further in my post there is a description of the experiment with polarizers and waveplates, corresponding to this model (CHSH inequalities). To understand it, you need to understand what polarization is. I have read...
https://quantum.phys.lsu.edu/old-website/seminars/abstracts/Kaushik10.pdf
I have discovered an experiment in the link above where you get NOON entangled states by mixing classical laser light with quantum light from SPDC. But I cannot understand the mathematics behind it. Can you explain it to...
Dear Anyone.
Please be nice and let me down gently, I know more about tapdancing than physics and I can't tapdance! It's just...
Kept reading nothing could go faster than light, in a vacuum (space.) So I Googled 'why' and discovered it's because things get heavier and heavier as they get...
hello
Einstein assumed the invariance of the speed of light as an hyphotesis, while I was told that :
"The speed of light need not have been postulated as an invariant."
in other words
the invariance of the speed of light could have been proven even regardless of the special relativity
is it...
Is there sufficient mass within the observable universe’s volume to form a black hole event horizon around the observable universe and, if yes would light fired tangentially at the edge of our observable universe ever loop back around in a circle or spiral inwards?
What is the difference between the GTR vacuum and the vacuum of quantum theory? What is the speed of light in the vacuums, specifically what can be predicted and what must be measured?
hello everyone
According to Einstein's second principle of relativity:
"The principle of the constancy of the speed of light: The speed of light in free space has the same value c in all inertial reference frames"
Does free space mean vacuum? Is this principle not valid in the air and the...
I'm trying to understand the Schram plot, which is the graph of wiki here: https://en.wikipedia.org/wiki/Cosmological_lithium_problem
I do not understand why the yellow box (the observed light element abundance) for H3/H (red stripe) is absent? Is there any reason for this?
I first thought that the angle would have to be maximum when it is closest to the critical angle for total internal reflection. From my lectures the equation for the critical angle is ##\theta _1>\ sin ^{-1} \left( \frac {n_2} {n_1} \right),## so as ##n_2 = 1##, we have ##\theta _1=\sin...
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As our universe is expanding, that is, our vacuum is becoming more and more sparse, I believe it is possible that some key characterics of our vacuum is also variable.
hello everyone
I read this text in physics book:
"Another example is the so-called Cerenkov radiation, which consists of light waves emitted by charged particles that move through a medium
with a speed greater than the phase speed of light in that medium. The blue glow of the water that often...
The equivalence principle tels us that we cannot distinguish between gravity and an accelleration. using that fact one can reconstruct the bending of light along the sun, but only half of it results from the equivalence principle together with the gravitational field around the sun. Is it...
Hello,
I have a problem with the postulate of the invariance of the speed of light.
When we move away from a light source it is redshift, it is the sign that the relative velocity between us and the light source has changed. If a stationary observer observes the phenomenon, he will measure that...
Assume two observers very far from each other, so far, that the accelerating expansion of the universe matters. (edit: But not outside of each others event horizons.) They will send light beams each other, and measure the energy of it. Also tie them together with a very long rope to fix their...
sir , i always taught what would happen to light traveling away from the mega sized star at the time of transformation of this star into a black hole? will it trace back its path after it taking a u - turn?
Hello and please know I am very greatful for your help!
I am wanting to learn how to measure light. I have chosen a specific light for this to help me better understand.
Lm- 7800
CD-620.7
So, I got that far, lol. I don't really know how to input the numbers for the Steradians equation, I have an...
I was a denizen of this forum some 15 years ago during undergrad. However I since joined the dark side working in software on ML, AI, and distributed data processing.
Every now and then I pick up a physics textbook to get into the weeds of a topic I would have missed due to skipping out on grad...
Hi Everyone! I have a photonics problem that I was wondering if anyone may be able to shed some light on (no pun intended).
I work for a company that is designing a fiber optic emitter/detector as a part of one of our products and we've noticed something that would appear to defy physics...
Imagine a plane 1 light minute across. Now imagine 1 person on either and of that plane. Between them, is a thin indestructible bar that is 1 light minute in length. In the center of this plane, a simple device has a wire that leads to a motion sensor on the left side of the bar. If the left...
https://en.wikipedia.org/wiki/Fluorescence
You normally heard of Fluorescence coming from UV which make the objects glow.
But visible light can also cause fluorescence. When you hit a colorful sample with a 532nm laser, there is fluorescence in the visible spectrum (as seen in Raman...
Are the Big Bang and inflation really needed to account for the large-scale structure of the universe, nucleosynthesis, baryon acoustic oscillations, and the anisotropies of the CMB? Can the universe not begin in an already expanded state and still have all those things happen just the same...
Hello !
I've got a problem understanding what are Lumens and how do I look at lux as well.
For example here :
It makes 800 Lumens in 1 m^2. Does it mean that in every direction in 1m^2 there are 800 Lumens ?
Or when I have a light bult with 800 lumens :
Those 800 Lumens in light bult...
While not having a professional physics background I was still interested in knowing more about special and general relativity. Therefore I was trying to find out where the space time interval was coming from in relation to the speed of light. Of course this is the first point to start I...
1) really does not make sense to me. It is not clear to me how light could be reflected in multiple directions if the source is not a tilted mirror or another object with specific properties. I think the thought of the "point" P confuses me. Further, the fact that light travels in the opposite...
Is there a way to create a map from satellites showing how much light pollution there is on earth? For example if you wanted to do astro photography and wanted to know how far away from city you need to drive to see certain levels of detail from galaxy?
Hello, I'm trying to focus a 275nm (with proper safety precautions) LED that looks to be a few mm in length and width (the light-emitting portion) to a smaller dot size. The LED should probably be fairly close to the surface of the lens to collect more of the light. The dot size would hopefully...
I have been given the task of modeling the heat transfer from a light source of known power into a system consisting of two connected materials. I must find the temperature change in the bottom surface. The two materials are initially in thermal equilibrium with the surroundings.
My first...
My Next DIY,
So, I'm guessing something like this may already exists (see image) light bulbs added for clarification purposes only.
Anyone know if there's something like this already on the market?
So, I did a google search for custom toggle switches but most if not all were for Marine or...
Does Ohm’s Law, V = IR work for light bulbs? It appears not to from my simple experiment below.
In the figure below, I measured the resistance of a lightbulb and found that resistance to be 2.6 ohms.
However, when I connect this lightbulb into the circuit where I measure the voltage across...
We can measure the two-way speed of light, but not, apparently, the one-way speed. Light could travel at c in every direction or c/2 in one direction and instantaneously in the other. Nature does not provide us with a way of determining the one-way speed.
I can follow some of the basic...
I get it, it sounds cool. But it is a very misleading and sometimes confusing way to represent c.
The speed of light is not constant. When I say that, I’m talking about the speed of LIGHT. Not c. Cherenkov radiation is a result of particles moving through some material (usually water) faster...
I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true? What keeps things of mass from reaching the speed of light or beyond? I assume matter doesn't accumulate higgs-bosons while in motion?
A ship that moves at a speed very close to light, its relative mass increases and may be comparable to the mass of the planets or the sun, in this case it can change the orbit of the planets and the sun (according to the law of gravity of two bodies)
Is this analysis correct?
The experimentally measured properties of protons and neutrons are known with exquisite detail. Our data is not quite as extremely precise, but still very good more other baryons and mesons with light quarks (u, d, and s) as valence quarks, such as pions and kaons.
Yet, on a percentage basis...
hello everyone!
Recently,i'm reading a paper about slow light,that's really a famous work published in Nature.[Light speed reduction to 17 metrespersecond in an ultracold atomicgas].
But I'm trouble with some calculation about the velocity of slow light.here are below:
i try to use the...
Is it possible to store large quantities of light for extended periods of time? If so would it make any sense to use it to propel a spaceship because it doesn't weigh anything? I read that one of the biggest issues with getting to space is the weight of the fuel.
I am taking a summer course on special relativity and I stumbled across this problem and solution which I tought look neat. However, I think the solution provided for a) there is wrong. I will here present two of my solutions for a) and one solution for b) and ask if you think mine are okay? :)...
Phase difference is $\phi=\frac{2pi}{\lambda}* \Delta+\pi$
Phase difference, max: $\Delta \phi=2pim=\frac{2pi}{\lamda_{max}}*2nd$
Phase difference, max: $\Delta \phi=2pim=\frac{2pi}{\lamda_{min}}*2nd+pi$
Flim thickness: $d=100nm$
Set the equations equal to each other i got a d=-100nm which...
Hello, I am looking for something a bit out of my wheelhouse today, gamma light sources (10 MeV or higher on the max energy threshold).
Does anyone here have experience or more information on these machines? Are they typically electron accelerators utilizing a tungsten or tantalum target? I am...
In special relativity I can get ## \gamma ## , ## \frac {T_B}{T_A}=\gamma ## Why do I not go ##{T_B} - {T_A} = \gamma## ?
##T_B = \frac {2H} {c^2 - v^2}## . ## T_B ## is the moving light clock.
## T_A = \frac {2H} {c^2} ## . ##T_A ## is the stationary light clockI assume LaTeX doesn't work...
I found that I had an inaccurate understanding of their relationship earlier. After rethinking, I try to express their relationship in a simple and understandable way
Nuclear reactions convert energy from form of mass to form of light, and both energy and momentum are conserved during the...
https://www.linkedin.com/in/hellandhansen/
CMO at an ophthalmological tech company; Bulbitech.
Now initiated an industrial PhD at the University of Oslo, supported by a Norwegian Research Council grant, where I will work on one of our tests (retinal adaptation speed to different lighting...
In doing a project on phototransistors I am using my smartphone as illumination source.
In order to find the responsivity of the induced current from the light, I need to know the surface power density, which I could estimate, if I knew the effective optical power of the light from the...
I'm quite aware that according to Einstein light is a particle and a wave at the same time.
However, I try to imagine how exactly would light expand. A photon must likely have a certain timing for expansion. I mean, after a photon is originated it immedialy multiplies itself into many other...