Light Definition and 1000 Threads

If light goes from air through glass, the reason the light bends is because I'm told that the light travels slower inside the glass. If I change my observer reference to inside the glass, the speed of light inside the medium it look like light is still traveling at the speed of light? if so, the...

I reviewed the derivation / solution of that GRT problem and do not see any dependence on the wavelength of the light. Is that correct, or am I missing something? This makes me wonder about my understanding of how prisms work. How or why do longer wavelengths go slower in glass than shorter...

Given that the universe is expanding, and we currently believe the universe as we know it began a little over 13 billion years ago, Then when we look at a distant object and say we are looking light from 10 billion years ago, How is that possible. With the universe expanding for 13 billion...

If you take two window screens and hold them, say, a couple feet apart and look through both of them, you see what looks like interference patterns. These types of patterns can also be seen in transparent materials when polarized light is passed through them. More on stressed materials and...

I always thought it was from individual water molecules absorbing and reabsorbing light, but this explanation in a video from Fermilab is very strange to me . What is this "new wave" he speaks of; wouldn't it be light too? If so, then this light is now slower than the speed of light, which...

During equal thickness interference, adjust the inclination of the two plates to expand the spacing of interference fringes to 10mm. Then, if a light with a width of 5mm is used for equal thickness interference, whether an interference pattern will be observed, and the width of the interference...

Suppose a light beam is sent from a distant star. When the light beam hit a telescope orbiting around the Earth. How is the light beam modeled? I have searched for many keywords without success. In my opinion, since the beam has gone so far, it can be viewed as parallel rays, with a decaying...

Where to look for a UV light that is invisible to the naked eye? Essentially I want to buy a UV light that doesn't have that annoying blue glow, I just want the UV light that is invisible to the naked eye like infrared light. I read a bit about it and from what I read what I'm looking for is...

Is there a material that allows visible light and uv light to pass through? Edit: A physical material

Googleing this question yields answers that don't really seem to address the core of my question. I apologize if I just haven't been able to see how answers are applicable, and would greatly appreciate any insight. Imagine a universe consisting of only our sun. no planets, no galaxies...

What other experiments, besides the M&M experiments confirmed the constant velocity of light? Thank you in advance for the response.

Could I please ask for help with the following question? Four uniform rods of equal length l and weight w are freely jointed to form a framework ABCD. The joints A and C are connected by a light elastic string of natural length a. The framework is freely suspended from A and takes up the shape...

My Cuisinart drip coffee maker has a light that comes on, telling you to run it through a cleaning cycle (50/50 mix water/vinegar, rinse). In our previous home, we were on a well of about 750 ppm dissolved solids (including some iron), so I had an RO unit connected after the water softener to...

Then the equation of motion for a photon in the beam (moving parallel to the ##x## axis) is\begin{align*} \ddot{y} = - \Gamma^y_{\mu \nu} \dot{x}^{\mu} \dot{x}^{\nu} = -[\Gamma^y_{00} + \Gamma^y_{xx} + 2\Gamma^y_{0x}](\dot{x}^0)^2 \end{align*}and similar for ##z##. In the linearised theory...

When we connect tungsten filament light bulb to the battery, filament becomes hot due to electrons losing kinetic energy in the electric field inside of conductor. Heat is eventually converted to electromagnetic radiation making light bulb shine. Light energy comes from flow of electrons and...

I tried using the equations above, but I wasn't really able to come up with an intuitive explanation. From my understanding, the electric field vector only varies in the x-y plane while the magnetic field vector only varies in the z-y plane. Also, both vary sinusoidally and both reach extrema...

It is sometimes said that a distant street lamp seen through a dark coloured umbrella fabric appears like dotted diffraction pattern, as in figure A. However, I have tried several umbrellas but all of them produce a blurred cross, as in figure B. The umbrella fabric superficially looks like a...

Two clocks with photo detectors are 100 kilometers apart at A and B. On the center of AB axis two light pulses are sent to the clocks , synchronizing them. Then a light signal is sent from A to B. The two stationary observers record the time from event at A to event at B. Is there a one way...

I am wondering if it is possible to use principals of diffraction to cause a collimated beam of light (laser) to become divergent. I see that zone plates are most always used for focusing the light from a source, unless they are used in reverse. This is why zone plates are seemingly always...

First off, I'm probably totally incorrect on all of this, so feel free to correct me. Second, I'm only 15, so please just be gentle and helpful when I'm totally off. Now for my idea: Have a huge vacuum and put lasers on the inside with hundreds of different lasers at different angles equally...

Why are gravitational waves able to move at the speed of light?

I was doing a exercise which considerst he time it takes for light travels a glass with thickness proper D and velocity v. The speed of light is c/n inside the glass. Now, my approach was to go to the glass frame, take the relative speed between the glass and the light using the trivial formula...

I wonder if this question is about two-point resolution or magnification... Would someone here be so kind as to offer some guidance on this question? Thank you!

I am an amateur in physics and I have a question. How does speed of an object affect time?

Hi everybody, I'm a mechanical engineer working on a phototherapy project, which includes choosing a LED light source that emits a spectral irradiance of 30 µW/cm^2/nm. however, most of the LEDs datasheets giving you the lumens at best. i was able to calculate the irradiance [µW/cm^2] from...

My question is: if you had no requirements for specific wavelength, intensity, duration, etc., are there ways of producing euv light (<150nm) without billions of dollars of equipment and power requirements in the KWs at most. Any Ideas?

i am having some hard time thinking about this problem: It is basically this: Imagine a bulb and a receptor distant L from each other (at the same axis x) inside a room, the roof of the room is at a height d from the bulb and receptor. Now you are at a train moving horizontally, parallel to...

Hi PF I've been twice to the dentist recently, and I've taken this picture. I don't find it in Google, and I know nothing about optics, but some words that appear at the textbook I'm now studying seem to be related: concavity, reflection, parabole...In few words, I'm more concerned about this...

I am trying to design an acrylic light pipe that has a 3W power red LED input with 60 degree beam angle. I need a reasonably collimated exit light beam or at least a narrow angle output. What I'd like to know is - what is the optimum shape of the exit end of the light pipe to produce the...

Einstein first calculated the bending of light rays that are touching the sun as 1.75 arc-sec. For the calculation I refer e.g. to https://www.mathpages.com/rr/s8-09/8-09.htm I know that spatial angles in general relativity don’t have an intrinsic value (are not invariant). They are dependent...

I know it's not possible to travel at light speed so this is just theoretical. As I understand it at relativistic speeds the distance you need to cover to travel to a destination are length contracted. If you were traveling at light speed is the distance between you and any object ever zero?

I'm trying to understand this paper and others on the same topic. I struggle conceptually with their first equation, which is an expression for an imperfectly phase modulated optical field from an electro-optic phase modulator (EOM) that is contaminated with a little bit of amplitude modulation...

Plant leaves only appear green because they absorb the red and blue wavelengths of light and reflect green away. Is there an intrinsic and innate reason for this that relates to the physics of light? Maybe green wavelengths are inefficient at storing energy in chemical bonds? Have plants simply...

We know the speed of light is a constant but speed is just the measure of distance over time. If blue light has a shorter wavelength than red but covers the same distance / time does this mean that blue light has actually made a longer journey than red light in order to arrive simultaneously? I...

If my eyes were sensitive to radio wavelength instead of visible wavelengths (and were large enough to resolve an image), what would the world look like? I assume that my brain would interpret different frequencies in a way that is analogous to colours, such that I could distinguish them from...

Some people thought light speed is actually instantaneous which can be demonstrated by doing an experiment involving a taut clothesline and two clothespins. On each ends of the taut clothesline, put one of the clothespins on both ends and touch one of the clothespin will make the other one at...

Summary:: If relativity causes wavelengths to change I.e the redshift effect (or blue shift effect for objects moving towards us) does the presence of 7 different colours denote seven different changes? If the doppler effect shows that direction of trajectory changes wavelength and colour of...

In Richard Feynman's book "The Strange Theory of Light and Matter", in chapter 2, he explains how to calculate the probability that light from some source will be reflected by a mirror and be detected at some location. He explains how you sum up all of the probability amplitudes (represented...

In particle terms I'm thinking this could be when the signal's photon density drops low enough to be indistinguishable from the vacuum energy. In wave terms, I'm thinking maybe either the amplitude or frequency might drop below any quantum threshold needed to budge an electron shell in any atom...

Do you have accessible web links discussing the pros and cons of the various theories of light propagation in dense media? I have done quire a bit of searching, but all seems rather superficial (Don Lincoln's video, f. ex.) Thanks

Let us consider a hypothetical scenario, where we are able to translate any mass at a constant speed of 10m/s w.r.t to a given frame of reference. For simplicity, we are going to assume that the object is at rest initially. Case 1 - Now, consider 2 points A and B at a distance of 10m, and our...

The universal speed limit is c, and as a consequence light is confined to that limit. I was thinking about the time dilation in SR and was wondering if this is result of reaching speeds close to the speed of light or because of reaching speed close to c? For example, let's say light could be...

Hi Folks, I promise there is an actual question at the end of this note. I couldn't see where to attach images on this forum page, so here is a link to a rough illustration and a photo of the project site in progress (the cabinet for the digester is partially built)...

I watched a Fermilab video on light propagation in water: . He says (~) at time 7:50: "The oscillating electric field of the light make electrons in the glass move. These set up a second oscillating electric field that combines with the first to make a single oscillating field. That is the wave...

Can electromagnetic radiations exist on their own without any source (i.e light existing on its own without flashlight). If light can't exist on its own so sources are necessary for light or any EM radiations in order to exist, how about the EM fields?

Here is a concept suggesting reactionless drive: Setup: A light pulse of wavelength l0 bouncing between 2 mirrors one on the left - ML and one on the right - MR. Each mirror oscillates perpendicularly to light travel direction attaining relativistic speeds vl, vr. Light pulse is timed so it...

This is one of my thought experiments where I am drawing a big blank, If you have 2 objects approaching a 3rd object from opposite directions (just enough off to avoid collision) at 75% of the speed of light, the first assumption is that each observing the other would see the other object...

There are actually several questions. The formula for calculating the "beam angle" of light (emitted from lights bulbs, flashlights etc) is - α = 2 arcCos ( 1 - Lm ÷ ( 2 π Cd )) Where, α = beam angle in degrees Lm = luminous flux (Lumens) Cd = luminous intensity (Candela) The above formula...

In the screenshots below there are the equations (11.49) and (11.53). I don't understand how did he derive equation (11.53) from Eq.(11.49)? From (11.49) I get: ##d\phi/dy= d\phi/du du/dy = (1/b^2-u^2+2Mu^3)^{-1/2}(1+2My)##. It seems he neglected the ##2Mu^3## since ##Mu\ll 1##, so ##y\approx...

Since an object's apparent mass increases as it approaches the speed of light, does it's gravitational forces also increases? (From a stationary observer's point of view)