Light Definition and 1000 Threads

The question: If the max speed I can go in the universe is the speed of light measured from? Background: If there are three rocks in a vacuum along a line (the x axis), one is stationary (rock 1), one is moving 5 m/s in the x direction (rock 2) and one is move -5 m/s in the x...

Hi Guys, I have attempted to solve the following question and was hoping someone can have a look and give some feedback. Any help will be greatly appreciated. Thanks! 1. Homework Statement Angler fish emit light through bioluminescence. An angler fish is swimming in a fish tank that has a...

Why does combustion emit light? For heat, for excited electrons or for other reasons?

How is it possible for different parts of a single rectangular wavefront to produce different intensity at particular point(P) despite the fact that wavefront is something which has all the particles at same phase?

Homework Statement Two thin lenses are placed 5 cm apart along the same axis and illuminated with a beam of light parallel to that axis, The first lens in the path of the beam is a converging lens of focal length 10 cm whereas the second is a diverging lens of focal length 5 cm. If the second...

If the concept of a wormhole is like folding a piece of space-time like a piece of paper, for near instantaneous travel faster than light, what is keeping us back right now? I am aware that it's really complicated and far beyond my scope of understanding right now, however I am fascinated by...

Other than relativity is there any theory, proof, experiment, etc. that tells us a photon has no mass? i.e. Is the concept of zero mass solely derived from relativity

Homework Statement Four identical wave sources (s1,s2, s3,s4 ) are located at the corners of a square. We know the phase at three sources: 0 at s1, π/4 at s2, π/2 at s3. Whet is the phase we have to give to s4 in order to have a maximun of intensity at the center of the square? Homework...

Hi everybody, I'm a curious worker and passionate student, I haven't got the possibility to study at the university but my passion for SSL lighting and light phenomena in general started some years ago, has helped me to start a long journey, trying to understand a little more day by day of what...

In school, I was taught that the position of an electron relative to the nucleus is only an approximation. It is very likely that the electron will be close to the nucleus and where it is 'expected' to be, but it may in fact be anywhere in the universe. Is this correct? And does this allow...

I have heard that LED light is not as good for growing plants as incandescent or fluorescent, can someone explain this? And what is the best color or wavelength to keep seedlings from getting all tall and falling over...? or is it the intensity?

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...

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