Light Definition and 1000 Threads

So I followed the derivation of the Macroscopic Maxwell's equations by averaging the fields / equations and doing a taylor series to separate the induced charges and currents from the free ones. But why does light now "suddenly" travel slower in dielectric media? I mean, sure, it comes out from...

While lying in front of a 500 degree woodfire, I wonder if besides light and heat that we take as ordinary does it also have ultraviolet rays of light like the sun?? What are the types from light from an ordinary on Earth fire?? Would they be beneficial to plants as main light source?, would...

Sorry, me again. In another thread #47 I gave a experimental setup to detect an anisotropy in light speed of the form ##c(\hat{n}) = c_o + \alpha (\hat{n}\cdot\hat{v})##. It was pointed out quite correctly that the error incurred in the long arm to the sensor would cancel the anisotropy making...

Does light exist between events? [mod: unapproved source] The above perspective will resolve a lot of paradoxes in QM. Is the above view viable or is it untenable? Are there any evidence to show that photons exist in flight? Are there any evidence of photon trajectories?

It's already known in physical communities that the velocity of light always constant and not depend on motion of observer or source. But it is also teached to us that there are aslo Doppler shift experienced by light wave like that when measuring CMB radiation. But for me it is makes a...

Mentor's note: this thread has been forked from https://www.physicsforums.com/threads/why-the-photon-has-no-mass.899792/#post-5912751 But momentum = mass x velocity so that part of the equation is E2 = c.(mv) If the mass is zero then that formulation also yields zero energy (which we know is...

Homework Statement It is just a conceptual doubt Homework Equations According to malus law intensity of light through polaroid is I=(Io)cos^2(theta) where theta is the angle between axis of polaroid and incident light. The Attempt at a Solution But when Theta=0 then I=Io but in my book it is...

When why sey that light is electromagnetic wave i understand this. But what i do not understand is where photons come into picture ? can somebody explain me the relationship between those two . My knowledge in this respect is not great so I would ask that the answers be adjusted .

Hello There:woot:, I have basic doubt about light propagation .So I'm hoping to get some help here. The problem is ...Let us assume two frames, 'MOVING FRAME'[one moving with a certain velocity(constant)] and 'REST FRAME'[one wrt to which the first frame is moving]. If now moving frame emits a...

Hi, What is people measuring when they measure the speed of light (c) actually? the photons or the waves? or some kind of manifestation of light? I ask because I was reading about photons and that they "might" have a very small mass and therefore are not traveling at c. If photons have a...

Homework Statement Find number of fringes separated by 1 cm on a screen at a distance of 2mm from slits which are 0.2mm apart from each other.The wavelength of light used is 500nm. Homework Equations The Attempt at a Solution I really don't know any way to solve it.I have tried putting unit...

Hi I have a personal art project and I am stuck, because of very limited knowledge. I'd like to project an 1-2 meter white line from 1-3 meter distance. The projected line should be as thin as possible (3-10mm) and as powerful as possible. I created a DIY projector, but my problem is that, the...

Does the eye's retina, rods and cones detect the E or B or both components of a lightwave? I've not been able to find much Googling. Thanks Hank

Homework Statement An angle is given between 2 polarizer's (45 degrees), through them light passes (unpolarized than after passing through the first one it polarizes), some of the light its shown on the display. For how much does the angle needs to be increased for the intensity of light to be...

Does anybody know where i can buy a device with which i can measure the frequency of light from various sources such as bulb light?

Hi All, An observer, F, stands on Earth. A spaceship, F', is also on Earth. Their clocks are set at 0. The spaceship then leaves Earth at .5c. After 10 seconds, F sends a light signal to F'. As soon as F' receives the signal, F' sends a light signal back. When does F receive this signal from...

Hi, so I was hoping to get an EE's explanation for what just happened. So my son was apparently over by the light switch pointing a UV pen light at the switch. Suddenly there was very loud, gunshot-like pop, sparks flew, and I had to go reset the breaker. Maybe correlation doesn't imply...

Hi I have a cheap smart phone with a low quality camera when I go to take a picture there is what I would describe as like old television static appearing in front of the image as it appears on the phone screen (although what is beyond it can still be seen). I am wondering if this is just dust...

Homework Statement Homework Equations [/B] apparently noneThe Attempt at a Solution [/B] Hi, this is a question from the OCR for self studying purposes. Only the first question is relevant for me. I know that the solution is 120N in the opposite direction to the weight, but i can't get to...

From Wien's law it is seen that approx 6500K(Greater than sun's temp) needed to heat a body to blue! But we see so much blue light(uv ray)! Are they formed from any different mechanism rather than heating?

What exactly is the physical origin behind light produced by Cherenkov radiation having a non-zero angle with the trajectory of superluminal charged particle? Why is the light simply not allowed to go in any direction? Also, is Cherenkov radiation observed for "uncharged" particles (e.g...

The velocity of light changes when it passes through a medium of a different refractive index. So let's suppose the light is traveling through a vacuum at a velocity c and then passes through a glass wall. Its velocity decreases while traveling through it but then speeds back up to c after...

I would like to start growing plants in an artificial simulated environment with very low cost, hence i would like to know whether if i could vary the wavelength of light using a normal led light by varying voltage or current

If the speed of light is ~300 m/s in a vacuum, can the electric and magnetic fields of the wave be condensed such that it travels faster? The idea being that an outside force condenses these fields and lenghtens the wavelenght with no loss of energy thus increasing the directional speed. The...

Homework Statement A uniform film of TiO2, 1036 nm thick and having index of refraction 2.62, is spread uniformly over the surface of crown glass of refractive index 1.52. Light of wavelength 515 nm falls at normal incidence onto the film from air. You want to increase the thickness of this...

Why the speed of light is constant for every observer ? Is it a special thing for photons cause I guess there's no other elementry particle that can move with c ? Also I want to investigate the constant of c for every observer, in the perspective of particle relationship. For example, can I...

Dear all, I'm studying a charged exciton system, composed by two ground states (electron spin up 1/2 and down state -1/2) and the two heavy hole trion state (up 3/2 and down -3/2). In this case the light which couples two ground states and the trion state has right/left polarization, to...

Me and my friend have recently (half a year ago) had a huge debate, between ourselves, about the wave-particle duality. We took sides in light being a particle or a wave. I was for particle he was for waves. At the end of a hot-filled week of arguing, the debate ended up with the acceptance of...

I've read that using a pinhole aperture and a wavelength filter can turn a "white" incoherent light source like a light bulb into a temporally and spatially coherent light source (albeit at low efficiency). Can a temporally and spatially coherent light source be made with a monoenergetic (or...

Hi! We will make a lab analogous to the stern gerlach experiments but with polarized light. How can we get only one single photon in experiment with a coherent light source? I'm going to make a lab where we need to get in only one single photo at a time. I have read that you can use some...

Homework Statement White light containing wavelengths from 400 nm to 750 nm falls on a grating with 6000 lines/cm. How wide is the first-order spectrum on a screen 2.0 meters away Homework Equations dsinθ=mλ for constructive interference dsinθ=(m+1/2)λ for destructive interference Δx = λL/d...

My book says that the Sun's rays reaching us are always parallel. See this image Are the Sun's rays reaching us always **PARALLEL rays**? I will be thankful for help!

Homework Statement You want to support a sheet of fireproof paper horizontally, using only a vertical upward beam of light spread uniformly over the sheet. There is no other light on this paper. The sheet measures 20.8 cm by 28.8 cm and has a mass of 1.70 g . (a) If the paper is black and...

Many diagrams show light cones tipping over when closer to a black hole singularity, such that emitted light can have a downwards (negative time) component in the distant observer coordinate frame. e.g this diagram: or this one: or this one: However, other diagrams show that the light...

Can anyone help me with a very basic question please. Is it really not possible for anything to travel faster than the speed of light, as dictated by relativity theory ? I am a complete beginner to Physics and only have very basic mathematics knowledge and I'm trying to understand the basics of...

I have been told the speed of light is constant and does not waiver. This would make sense as light has no mass I am aware of. Pictures taken during a solar eclipse seem to prove gravity bends light. Could it be however that the light is not bent, only the time/space light is traveling through...

So I was wondering that why does time move slower the faster you get ? And does it happen at all or is this is just fake ?

If I say that a star will die after 50 million light years, can I also say that that after 50 million EARTH years, the star will die BECAUSE DISTANCE AND TIME ARE INTER-CHANGABLE (if a airplane travels from point A to point B and the distance is 200 miles, I can also say that the distance is...

Homework Statement I'm a new physics teacher and was teaching about polarization of light today. A student asked me a question I wasn't sure of the answer to. Let's say you have two polarizing filters stacked on top of one another. The first filter is held so that the spaces in the filter are...

Scientists are exploring new states of light with orbital angular momentum https://futurism.com/harvard-scientists-made-material-creates-completely-new-states-light/ Research paper http://science.sciencemag.org/content/early/2017/11/01/science.aao5392

I would like to know whether my thought is right or wrong about time dilation example. Let's say, A person is standing at a starting point so his velocity is 0 ms'1. A car runs from that point in the velocity of 3 ms'1. A photon from a light source at that point is also emitted at the same...

As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to...

I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).

I may have a fundamental misunderstanding of the concept, but I was wondering, how does the accelerating expansion of the universe calculate for the time dilation in light travel? From my understanding, we know that the universe expansion is accelerating because the farthest galaxies that we...

Homework Statement I have an equation to solve. See the attach pichture. I(r,φ,λ) = I0.sin(2πr/R).sin2(φ).(1/λ) where I0 , R are constants r,φ are cylindrical coordinates 0≤r≤R/2 : the cut is laterally limited λa ≤ λ ≤ λb : the beam contains a limited frequency spektrum where the shortcut for...

Hello from Belgium. Bruxelles. In 1815, Fresnel made, with Arago, the experience of Poisson spot. (or Arago spot, or Fresnel bright spot). A bright point that appears at the center of a circular object's shadow due to Fresnel diffraction. Arago and Fresnel glue a round opaque screen on a glass...

Dear all, I am currently doing a project about the light trajectory near Schwarzschild black hole. I wrote down a couple of differential equation and I have created a C++ program hoping to solve the orbit of light. However, the program results turn out to be quite weird. The differential...

Hi, Can someone please explain as to why light beams attract or repel each other even when they don't have charge. Seems like it behaves like two current carrying parallel wires. There is very little material about this which goes completely above the head. Thanks

A) Can the light of a laser be trapped by a spherical mirror. B) would it help to have a liquid in the sphere so as to distribute this light equally throughout the volume of the sphere. Assume laser is shown in the internally spherical constantly. The key is that we want this light to remain in...

Homework Statement Homework Equations Weight = Tension in y direction?? The Attempt at a Solution I thought that W = the tension in the y direction of the two cables so that T2y and T1y are both 20 N each. Thus, i calculated that the tension in AC is 33 N ( cos(53.1) = 20/T1 --> T1 = 20/...