Light Definition and 1000 Threads

Was shaving just now and one of my mirror wall light bulbs blew up. Luckily it's encased in the light fixture with an opening at the top so it was contained a bit, but some glass blew up through the top and rained on me. The glass was very hot, so I'm guess it wasn't LED.

d)NONE OF THESE

[Mentors' note: Split from https://www.physicsforums.com/threads/is-there-a-thought-experiment-to-show-that-the-speed-of-light-is-constant.986641/] If I could provide you with a device to measure the speed of light, and the accuracy can reach 0.01 m/s, what would you do?

I'm studying particle counters and one of the detection methods uses reflected light to determine the sizes of the particles. What principle does it base on? Thanks!

I know the amazing thought experiment by Albert Einstein with the two light clocks. (The observer at the train station has a light clock and the person in the train.) It's amazing because you can even deduce the formula to calculate how fast the clock in the train goes. But this experiment...

Looked upon this and can't seem to find anything. The formula I=Icos^2theta seems to only work for polarization filters, which is not this case. On the other hand, the brewster's angle only c.aclates the angle when the REFLECTED light is polarized, not the REFRACTED light. Hence I am confused...

On the photo you can see: Red 1: the edge is very sharp (as expected) Red 2: the edge is very blurry (but why?) Same for green. You can also see (Red 2) that the blurry edge is yellow. What is this effect called?

Not to get off subject but, when I gaze at the Triangulum Galaxy how “Old” is the light I’m observing?

I was wondering if it would be possible to see the history of space if one was to stand at the edge of the universe as it expanded faster than the speed of light. If the universe was to be expanding faster than the speed of light right now, and I was able to somehow go there and keep up with it...

A lighthouse is located on a small island 16 km off-shore from the nearest point P on a straight shoreline. Its light makes 5 revolutions per minute. How fast is the light beam moving along the shoreline when it is shining on a point 3 km along the shoreline from P?

As much as i search Google, in an effort to find out how exactly the constancy of speed of light was historically deduced before 1905, from Maxwell equations or by any other means, i am not able to find such an explanation. In all of the search results that i could find, it is just stated that...

I have only seen Fresnel and Franhoufer diffraction being discussed in textbooks. Is it because they are the only two tratable types of diffraction? I mean, in the sense that one can really work out the equations to get results.

I've always thought that light could possibly be transmitted faster in one direction than the other depending on the velocity of its container - despite what the current understanding of physics says! The problem is that its very hard to prove, and to this end I've read through all the...

How do two highly directional, orthogonal light beams (or any other kind of waves) with the same frequency interfere with each other?

Hi, I read various threads in PF about the concept of invariant speed and the speed of light in vacuum that in our universe happens to be the same as the 'invariant speed'. My doubt is about the speed of the light in vacuum as measured from a non-inertial frame (basically in the context of SR...

My answers are quite different and here are my attempts a) What is the spatial separation ##\ell'## between the point of emission and absorption? (In the frame going ##v = \beta c##) From what I know is that moving causes lengths to be contracted according to the formula ##\ell_{travel} =...

Which one does it mean: "phase velocity" or "group velocity" or "speed of the wave front"? In the postulate of constant speed of light .

The concept of that when a photon's trajectory intersects with the Schwarzschild Radius/event horizon, said photon will never exit the Schwarzschild Radius/event horizon. Or any other object besides a photon for that matter. So far what has been the strongest evidence for this prediction?

What is the equation/formula for the Speed Of Light? E=mc²? I thought it would be simple to find in a search.

In our galaxy, two stars, A and B, move about 20 km/s in slightly different directions to each other. The stars are about 15 light years apart. Initially, the light beams are exactly anti-parallel. Will light beams emitted from star A traveling towards light beams emitted from star B stay...

The phys.org summary had me intrigued and the resulting new paper makes for heavy reading at my level of knowledge, but it was the underlying reasoning of the methodology that I really question: One of the authors notes "It's so rare, that they should not have seen any." From that, the...

5.879e+12. So that is what comes up if you convert one light year to miles. My question is, what does the 'e' mean? I see it quite a bit.

I don't even know where to start with this problem. What kind of slit makes linearly polarized light circularly polarized? The correct answer is d = lambda/(4(n1 - n2)) = 856nm. But how do I get there? Thanks in beforehand!

Hello everyone! Let's say that you were to attempt to go as fast as possible on a spaceship with the mass of an average car in an absolute perfect vacuum. What I am wondering is, that if you were to reach a certain speed, and stop applying energy to this imagined spaceship, would the spaceship...

Hi :) I just had a (most likely totaly unoriginal) thought and thought I should try to ask someone who's thinkings on physics are somewhat more refined than mine. So after thinking twice about private messaging Mr Tyson and Mr Cox :) I decided to google 'physics forum'. So here I am with my...

I'm in Surrey, London, UK. I've noticed this stationary light in the sky near the moon when there are no stars visible. What is it?

Isn't the meaning of speed, a variable of distance divided by a variable of time? Therefor isn't the meaning of a constant speed of light, a constant distance divided by a constant time? If there is any truth in this saying and there probably isn't, then what is the meaning of light constant...

If i am moving away from an object at a certain constant speed close to the speed of light, is that object also moving away from me at the same constant speed?

Would it be correct to say, that we are moving away from stars at the edge of the universe, at the same rate that these stars are moving away from us? I am relating to stars that are moving in relation to us, at a speed that is faster than the speed of light. Is the symmetry that maintains that...

To describe the movement of the planets, Newton assumed that there was such a thing as gravity. But he didn't know what gravity was. To derive the Lorentz transformation, Einstein assumed that the speed of light was absolute (not relative), but is it also known why the speed of light is absolute?

If space is transparent how can we not view light from a black hole

I ran into something on a non-technical message board that is familiar to me - a poster, clearly without any scientific knowledge, saying that Relativity is wrong. Unfortunately, the point he used as a battering ram is one to which I don't know the answer. He suggested that the light...

I understand that the meter is defined from the speed of light (distance light travels in 1/299792458 of a second). But how did man measure this exact distance to this level of precision? With any apparatus, isn't there an unknown amount of bottleneck somewhere?

I need to enlarge the light produced by a small laser beam that I have for a science project. I can't buy a larger laser because they're too expensive and not in the right color. Any suggestions? Thanks!

Is there any reason to believe that the one way speed of light is constant? Not isotropic, but constant in the sense of being independent of position.

"When electrified rods are brought near light objects, a similar effect takes place. The rods induce opposite charges on the near surfaces of the objects and similar charges move to the farther side of the object." -from a high school physics book. NCERT Class 12th part 1 to be precise. can...

I think that what happens is that the amplitude becomes sqrt(2)/2A in the slit filtered, as opposed to A in the other slit. I suppose we will still get constructive interference from the slits, so the value (1+sqrt(2)/2)A will be reached as opposed to 2A in the usual experiment. However, the...

How to calculate the wavelength of light coming from 1 light year away. Is there any formula for it. Please help.

The parabolic mirror pictured below is such that all incident rays, neglecting diffraction, are reflected towards a focus. A question states that the light cannot be focused to a point precisely, since there exists a circular diffraction pattern in the focal plane. The following diagram is...

I have A2 as 150, A4 as 150, A5 as 300 and A3 as 0. I just need these answers checked to make sure I’m right.

Hi all! Breaking down the question bit by bit: AC is coated with a silver film which acts as a mirror - Okay, nothing as of yet right..? A light beam is an incident onto prism at Point Q such that angle PQB is 40 degrees - This means that my incident angle is 50 degrees as shown below...

I take the following example to explain my question : when a « black-hole » is attracting a planet there is a Force which is proportional to the 2 masses and inversely proportional to the distance between the 2 masses. When the planet moves towards the « black-hole » this attraction force...

In A.P. French's Special relativity the author said, The mass and length of the box are irrelevant here. He said the momentum of the radiation is ##E_{radiation}/c##. We know that the momentum of a single photon with energy ##E_{photon}## is ##p_{photon}=E_{photon}/c##. So is...

Hello, Light, laser or not, is fundamentally electromagnetic radiation with visible wavelengths. Laser light has both high spatial coherence and temporal coherence (highly monochromatic) while regular light has both very low spatial and temporal coherence. Spatial coherence is not about spectral...

Hello to all, In a short pulse laser emission setup, can a pulse be emmited with beam length shorter than one wavelenght? (can a pulse have a duration shorter than its period?) Lets say a laser emmiter shoots a quarter cycle pulse, what would happen to this short beam? (lets supose the...

Imagine that we have an electromagnetic wave or light propagating in x direction, and \mathbf{E} is oscillating in z direction and \mathbf{B} in y direction. The picture looks something like this Now, if there exists a charged particle q on the xx axis at rest, then our B field can't do...

When we say speed of light = c m/s. Who is measuring meters and second. From SR perspective, that photon is moving towards you at speed of light so there should be time dilation, correct?

I set up the equation .5((cos 12)^2)^x = 1/9 Solving for x gets me 34.037 34 + 1 = 35 I've entered answers of both 34 and 35 and both have been marked as wrong. Does anybody know what I'm doing wrong here?

A thin lens has an upper radius of curvature 𝑅1 and a lower radius of curvature 𝑅2. When the lens is completely surrounded by air, it has a focal distance 𝑓. The lens is then placed in the interface between air and water inside a vessel (see figure). Calculate the refractive index for the glass...

In the process of trying to understand holography I encountered a detail that I kind of knew before, but just now I realized I have no idea how it works, how is it even possible. I’m talking about a simple pinhole camera where supposedly no matter how tiny a hole is a beam of light would still...