Light Definition and 1000 Threads

Radio wave travels at the speed of light 3x10^8 (m/s) Converting the distance to meter: 1.3 x 3.1x 10^16 = 4.03x10^16m The time it takes in our Earth frame of reference is: 4.03x10^16m/3x10^8 (m/s) = 4.26 years The answer is B But wouldn't the time in light's frame of reference be 0 and it's...

When traveling into an optically denser medium, the speed of light reduces and as per the principle of least time, light bends towards the normal and takes the shortest path. But why isn't this followed when light passes into a rarer medium? With its speed increased in the rarer medium, if it...

I know that there are at least a couple of threads related to COVID-19 scattered over PF, but I want to get a specific feedback on this latest research in terms of human health and safety. This paper was published in Nature, and it presented a rather fascinating result if it is true. The...

Hi everyone, been reading this site for a while, and this question has been stuck in my head for 3 days and i can't shake it, so i figured I'd step out of the shadows and ask. There are some follow up questions that came on the same train of thought too. Can light pass by a Black Hole and get...

I feel like the emerging idea of quantum communications; is that you can exchange data via the synchronous states of entangled particles, across any distance, in real-time. But, there's also this dilation in the physical world, at the speed of light, according to relativity. So- how would the...

light is electromagnetic wave ,so does it also have magnetic and electric field,like all others waves(micro,gama,xray,radio waves etc..)? i never heard that some one talk about light in sense of magnetic and electric field.. if it has ,why than compass don't response to light?

My Basic Question is- Why can we see our inverted and real image inside a concave mirror when the image is formed in front of it and not behind? If you say that our eyes tries to image the real image formed by mirror on the mirror itself then- Imagine a situation where we have a concave mirror...

Hello! I recently had a discussion with a person who's well-read on quantum physics and I was suprised by his claim that "light is in no sense regarded as a wave" in quantum mechanics. His support for this claim was that there are no wave crest or wave trough, there is nothing moving. What...

In this article it discusses the generation of something called super chiral light and claims with metamaterials they can make it have very high angular momentum like l=100. What does that really mean? How does that relate in magnitude to the normally computed linear momentum of a photon p=h/λ...

I was curious if the relative speed of an object can exceed the speed of light. Specifically, I am curious about the following thought experiment. I am not a physicists (and if I were asking the following would make me a poor one) and it has been 20 years since college physics. If a vessel is...

Hello, everyone, I have a LED, 620nm, with a viewing angle of 20°. I would like to bring this light in a distance of about 20cm on a lens with as many photons as possible. My idea is to position a converging lens between the LED and the lens. To be exact, I would position the lens at the...

My initial guess... Third dark fringe is 2nd order dark fringe and second bright fringe is 1st order bright fringe. Is this the correct guess?

In the above diagram, I have illustrated what is written in the summery. So, if the thickness and refractive index of the material are chosen such that the part of the wave that travels through the slab acquires a path difference of λ/2 and at the right end if I keen another convex lens so as to...

As you all know: Planck evidence for a closed Universe and a possible crisis for cosmology https://www.nature.com/articles/s41550-019-0906-9 If confirmed, it would bring back the Big Bounce as a possible hypothesis for the evolution of the universe. This has long-term consequences being that...

Do any animals see in a spectrum other than visible light and infrared?

Hi All In discussing another issue it occurred to me the only experiential evidence I know that normal visible light is EM radiation is Faraday Rotation. I strongly suspect we have a lot more these days. Amusing story. Fermi's wife had a degree in general science that did not cover...

Hi thereLet’s consider a photon of wavelength λ is being reflected across of gap d meters. The photon is a reflected back and forth between the same points on two horizontal sheets that reflect 100% of the light. What happens when the distance is smaller than wavelength? Thanks

I purchased a RadiationD-v1.1(Cajoe) geiger counter off ebay, and attached an arduino nano and a 16x2 display ( I got the instructions off this site https://www.instructables.com/id/Arduino-DIY-Geiger-Counter/). I noticed that the counter was sensitive to UV when I had it out in the sunlight, so...

I was reading (or at least skimming) this paper: https://arxiv.org/abs/2005.10702 in which they seem to be discussing gravitational wave lensing. Is this an analogue of light lensing or is it another subject entirely? I mean, as I understand it, light is bend using gravity (as for...

Has anyone here heard of the the HTLGI festival? Is anyone attending?

The size of light beam is same or different before and after refraction from a medium. If same then why we can not prove from mathematical expression. If not same why?

Hi, Would it be correct to say that at Brewster's angle, all the incident light which has its electric field parallel to the plane of incidence gets refracted, and the rest of light whose electric field is perpendicular to the plane of incidence gets reflected? For example, if the light whose...

I apologize if this question is in the wrong forum section - but I could not find a proper place for what is a basic question or perhaps a nonsensical one. Is the reason why an object cannot travel faster than the speed of light because the object itself is ultimately made of waves? Is the...

In my latest 10th grade physics lesson, we were learning about the refraction of light. I decided to share what I knew about why light slows down in a vacuum, which is, in short, because the electric field of the electromagnetic wave exerts a force on the charged electrons of a medium, which in...

Time as we perceive is not a universal constant. It depends on the speed of the bodies and the distance between them.

My guesses are that if slit is almost closed, then the width is comparable to the wavelength and diffraction will occur. does this means that he will observe the slit S clearly or less clearly? [Picture cleaned up a bit by a Mentor]

Hi, I have a 25w 254nm bulb ozone free UVC bulb (draws about 19watts from my kil-a-wat). This was purchased from amazon, produced in China. This light definitely omits a funny smell, it pulls 19w, and the glow in the dark stickers are illuminated after my test (so I know it is omitting some...

There's an undergraduate physics course at my uni that covers these topics and the course description is: Mathematical descriptions for classical physics: oscillations, mechanical waves, electromagnetic waves, physical optics and thermodynamics. Are there any good studying materials/textbooks I...

so I was recently studying some ray optics and then suddenly a weird question came across my mind I just don't know if it's the correct thread to ask but let's continue anyway So the question is : suppose there is a spaceship traveling at light speed and someone fire a laser inside it what...

Looking for a beginners explanation to the following question: How is Doppler effect separated from the original spectrum of light emanating from a moving body (in astronomy or other physics branches)? If the question does not make sense, here is the reasoning to ask it: If a certain color is...

Light consists of transversely varying electric and magnetic fields. A point charge in the path of a vertically polarized light beam experiences a vertically varying force from which energy can be extracted. In an unpolarized beam, the electric fields of individual photons act randomly in all...

The setup of the problem is shown in the image below. I know that I must add all the contributions of each reflected ray and that its amplitude will be reduced by a factor ##r## each time it is reflected. So after the n-th reflection, its amplitude will be ##E_0r^n##, with ##E_0## the amplitude...

I've been playing around with this for quite some time now this morning but can't get the last bit out. I defined the time functional to be $$T[y] = \int_{x_1}^{x_2} \frac{\sqrt{1+(y')^{2}}}{c(y)} dx$$ which follows from consideration of the time taken to cover an infinitesimal section of arc. I...

The doped a-Si: H layers in a HIT solar cell do not contribute to the photocurrent. The light they absorb (according to their absorption curve below) is lost. For a doped a-Si: H layer at the front side of the cell that is 25nm thick, what percentage of light at 400nm will be lost due to...

In my drawing you can see: A generic bulb covered by a mirrored hollow ball. The hollow ball has a small hole (1 mm diameter). So the complete light will go through this small hole. The lens will bundle the light in a very distant (100 km) focal point. I guess it might be hard to create such a...

I've read a couple of other topics on the Physics Forums about the lumped circuit abstraction requiring that signal timescales (i.e. the period of the highest frequency signal component) be much longer than the propagation delay of the signals though the circuit and that the wavelength should be...

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?