Tag Info

1

I hope that the image below may clarify the situation. Laving aside formulas, let me refer to the concept. Coherence length $l_c$ of a wave-packet is the length of the wave-packet along which its wave-length is stable. The longer $l_c$, the better is for our interference experiments. Let me explain. Please see the figure. What we do in experiments as ...

10

The video you show is of a liquid crystal display (LCD) monitor, also known as 'TFT'. The 'trick' depends on the specific design characteristics of these monitors (described below) and will not generally work with other types of displays such as LED and PLASMA displays. All liquid crystal displays (LCD) operate on the principle of being able to 'twist' ...

-1

Provided that the electron & the atomic beams also exhibit refraction,it seems that this is a particle's property.This is Newtonian explainable:you can see it if you are shooting the seewater with a machine gun.Deflection angle is proportional to the friction (depending on particle's mass/size and the medium's density).Photon behaves as particle in this ...

1

I think what you are asking is why a ray is refracted towards the normal when it passes into a medium of higher refractive index and why it refracts away from it when it passes into a medium of lower refractive index, i.e. and intuitive explanation of why light obeys Snells Law. You can really only accept it if you accept that even a single photon is a wave ...

2

Reading some of your earlier comments, it seems that there is a slight confusion at play here. From a comment on the original question: I want to know how these photons are sent in that parallel order. As I understand or imagine, photons should be thrown randomly from Sun's surface. Technically, you are correct: photons - including streams of photons ...

3

The Sun rays are not exactly parallel. They seem parallel as "Phonon" says, see her comments, but at a precise examination they are not so. Are you aware of the Hanbury Brown Twiss experiment? Look in Wikipedia at the site http://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect, and see the lower picture in that article. I copied the picture below. ...

0

Light from the sun actually converges on the earth - the sun is about 220 Earths across, so light from one edge and light from the other edge must converge to reach the same point on Earth. The angle is small enough (about 0.5 degrees) that for most practical purposes we can consider the sun to be either a point source or a uniform flat source as needed.

0

Suns rays are isotropic, but if we assume a small area $dA$, then the rays would be perpendicular to that crossection, and parallel with eachother.

0

I suspect Austin was just wondering what it would look like if we could see radio waves. The best analogy I can think of to represent that is to put an arc light from a carbon arc search light without the shroud and reflector on the top of the antenna pole and apply the same wattage. The main difference is that the electromagnetic field of the radio wave ...

1

Your two questions are based on the erroneous notion that light looses energy in going through a glass slab. Light has a propagation speed which depends on the density of the medium. When a light beam goes from vacuum (air) into glass, the only thing that happens is that the wave gets delayed (takes more time to travel the same distance, because of the ...

0

I'm just going to add something orthogonal to Floris' correct answer, because the question is posed in a very general manner, which allows for relatively diverse yet correct kinds of answers. Here's a crude-intuitive way of seeing it: A wavelength is just the spatial period of a wave, be it of mechanical or electromagnetic nature. Meaning the distance ...

1

In principle, a wave of any size will interact with a system of any size. The question should therefore be posed differently: how is the interaction of the two affected by their relative size? Let's take the simple example of scatter. You are familiar (whether you know it or not) with Rayleigh scatter - it's an elastic light scattering phenomenon that makes ...

-4

Radio antennas generate electromagnetic fields. Light is a physical particle of energy called a photon. Since the the radio antenna doesn't generate particles of energy, no matter the frequency, it can't produce light. The flow of current in a conductor generates an electromagnetic field that propagates from the conductor. The generating of photons from an ...

0

Not completely clear what you mean. You can't completely remove the electric or magnetic field - an electromagnetic wave needs both! Light with no particular polarization can be thought of as an equal mixture of light with polarization at right angles to each other, but both in a plane that is perpendicular to the wave motion. However, when you pass light ...

0

I think it is easier to think of, in the case of a linear polarizer, as it aligning all the electric fields to one axis. After the light goes through it the electric field is aligned to one particular axis and the magnetic field will be perpendicular to it. The electric and magnetic field are required for the propagation of light. Essentially an ...

-1

What I know is that for polarizing an atom, i.e. creating a dipole, we consider the wave-length of the e.m. field greater by a couple of orders of magnitude than the dimensions of the atom. Does it mean that we test the atom? On the other hand, if we study the structure of a crystal, we send on it e.m. waves of $\lambda$ bigger than the distance between the ...

0

If speed decreases at constant frequency that means obligatorily that the wavelength must diminuish. Your circular reasoning does not consider that the equation's inverse proportionality depends on λ. Example: If frequency is 1 MHz (1.000.000/sec) and wavelength 1 μm, the velocity is 1m/sec. If wavelength decreases to 0,5 μm, velocity is diminuishing to 0,5 ...

-1

The relation velocity equal $v = \lambda\nu$ is a natural relation. As frequency is number of waves passing a point per second and Wavelength is length of each wave so on multiplying these you get the distance covered i.e. velocity. And It is rule of nature to keep frequency of light constant on changing medium(ans for 'why' I believe it is not in scope ...

1

Assuming when you say the output is "dispersed" you mean it is incoherent and radiating in all directions, what you are asking for is a fluorescent material. A Google search for "IR fluorescence" finds a couple of companies making these materials for biological sample marking, however the ones I checked into further need a slightly longer excitation ...

2

I found a link for halving too: Nonclassical light generation in the process of self-frequency halving in a periodically poled active nonlinear Nd:Mg:LiNbO3 crystal Nonclassical light generation at self-frequency halving in periodically poled active nonlinear crystals is studied. The squeezing spectra of fundamental radiation and its subharmonic are ...

2

Yes it can be seen, rainbow can be considered as a set of points which form an angle of $42^{\circ}$ with the sun and our eyes, which comes out to be a perfect circle with center at our shadow made by the light coming from the sun. Usually we see a rainbow from ground and from there these set of points form a semicircle in the atmosphere. But if we observe ...

1

Light is the visible part of the electromagnetic radiation and consists of photons. Each photon has an oscillating electric and an oscillating magnetic field. In vacuum both fields are perpendicular to the direction of the photon's motion and perpendicular to each other too (see this sketch). There are mainly two used by people opportunities to increase the ...

7

I'm imagining a box made completely out of anti-matter so that your situation is realistic. Positrons are the antiparticle of the electron (i.e., the anti-matter equivalent). Meaning, in this case, they're identical to electrons except for charge. Photons, though, have no charge. So don't give a hoot whether a charged particle it's interacting with is ...

-1

At any particular point in space, there is only one value for the electric field. Of course, if multiple electromagnetic fields are overlapping at that point, then their electric field components are added together to yield the total electric field (this is because electromagnetic fields combine with linearity). When multiple electromagnetic waves overlap ...

0

You'll find a number of images on the internet such as the one below that claim to be a 360° rainbow. Most of these supposed rainbows are not rainbows. They are instead "glories" (wikipedia article). The image below is from that wikipedia article. Rainbows are much bigger than glories. A rainbow, like a glory, naturally is a 360° optical effect. You don't ...

0

Take a hose that sprays water in fine droplets and direct it towards a bright object like the sun or a lamp... instant 360 degree rainbow!

2

For the conditions to see a part of a rainbow, I would say you need the following: sufficient moisture to form numerous micro spheres of water, which creates the refraction pattern the right angle between the observer and the sun sufficient mass-thickness with this angle and with this composition to build up a visible amount of color Since the sun is ...

2

Its all upto the relative position of the observer and the sun. The imaginary line connecting the centre of the rainbow and eye of the observer called the line of vision makes the apparent struture of a rainbow. If the line of vision is a straight horizontal line with respect to the surface of the earth. You will definitely see a 360 degree rainbow. I ...

2

As an experimental particle physicist I stick to observables . The complicated mathematical functions which have been established as necessary to describe the quantum mechanical state function of the particles under consideration are not observable. By the postulates of quantum mechanics the complex functions of space time or energy momentum are not ...

0

Although you can (as you obviously know) think of electromagnetic radiation as either a particle or a wave, it's easier in this case to think of it as a wave. As a thought experiment, if you wave a magnet near a piece of wire, an electric potential will be induced in the wire. Likewise, if you pass current through a wire, a magnetic field will be produced ...

0

There are two scenarios that come to mind. 1) the universe as it exists now, with only the propagation speed of photons instantly becoming infinite. 2) The speed being infinite at the start of the Big Bang. For the first scenario, since light that we don't see now would become visible, the sky would become at least as bright as our daylight sky. Since all ...

0

According to the cited article Zitterbewegung is "a theoretical rapid motion of elementary particles". It never was observed. But let us say, that Zitterbewegung is real. The emission of photons is, or the reaction of an higher energy level of this particle to his environment, or takes place during acceleration processes. How ever, the particle get a higher ...

0

Your question is pretty vague, but does this help-- The E-M wave amplitude is a complex oscillating function, as you can see at the wikipedia page . Now, the power in any wave is the square of the amplitude, or more precisely, the product of the amplitude and its complex conjugate. It turns out that E-M energy is quantized, so we can assign a specific ...

11

A classical explanation to supplement Rod's excellent quantum mechanical one: If you make a Huygens construction of wave propagation (I assume you know how to do that) then every point on the wave front is treated as the source of a new wave of the same frequency and phase. How that wave propagates depends on the medium it encounters. So the Huygens ...

45

When light is propagating in glass or other medium, it isn't really true, pure light. It is what (you'll learn about this later) we call a quantum superposition of excited matter states and pure photons, and the latter always move at the speed of light $c$. You can think, for a rough mind picture, of light propagating through a medium as somewhat like a ...

1

Simply because two light rays intersect at a point it does not mean that an image is formed. You need millions (not necessarily, but a lot) of light rays to intersect at a point to form an image. The reason is that the intensity of light emerging from a two-ray intersection is too less for any human eye to detect. For an image formed due to a concave ...

1

Assuming you want to notice that there is a mirror on the moon, the question comes down to the resolving power of the human eye. Let's assume a healthy person with 20/20 vision. When looking at the moon, their pupil is dilated - say 6 mm diameter. The angular resolution of such a pupil is given by $$\alpha = 1.22 \frac{\lambda}{d} = 1.22 \frac{500\cdot ... 1 Provided that there is nothing for the photon to interact with (i.e. we look at it in vacuum), the mean free path will be infinite; that is, it will continue travelling forever in a given direction. There's nothing which will stop the photon's path. Hence, it will go arbitrarily far. Whether you have a single photon or a laser, the answer won't change. The ... -1 You would get more 'photons per second', which is photon flux (not intensity). Strictly speaking, the light intensity is the power of electromagnetic radiation incident per unit area on a surface, known as irradiance. This is a function of the energy of the photon E_P, so would vary with wavelength \lambda, where:$$E_P=\frac{hc}{\lambda} So If one ...

0

Much of scattering theory falls under the heading of Mie scattering. It examines how light scatters off uniform spheres with a given electromagnetic permittivity. In fact, it provides exact solutions to Maxwell's equations in this case. The original work was done in Mie 1908 (in German). Various further approximations can be made, leading to things like ...

0

Newton's first law states a particle will have constant velocity unless an external force acts upon it. The photon has no mass, but nonetheless the first law still holds true in the case of light. When a ray of light is projected, (say) from the surface of Earth to outside in space. The condition is that, there is no obstruction to it till infinity ...

1

As soon as the universe came out of its dark age if light speed was infinite then it would be able to keep up with the expansion of the universe. It would be very much brighter all around, perhaps intolerably to us. The universe would appear very active since event far far away would appear to us instantly. We might be blind as our light sensory organs might ...

0

The distance that a particle can travel is partly set by its mass. If the particle has a mass less than something like 7 eV, then it could cross the universe without attenuation.

0

The purpose of a negative is to allow the correct wavelengths through. For example, to produce red, you make the area transparent to red, and opaque to other colours. Then, white light shone through the negative would produce a true-color image. In RGB terms, if the red colour was say, 192, the negative would be 63, and white light at 255 would be ...

0

The expansion of space due to "inflation" is considered to be the cause of significant redshifts that is observed. It is sometimes referred to as a "Cosmological redshift", and is described with the appropriate equations.

0

Whether it be a beam or ray of light, photons will keep traveling until they are absorbed. Photons can't stop because they travel at a constant velocity, the speed of light, i.e., they can't accelerate or decelerate. However, their wavelengths change over time due do the expansion of the universe, i.e, their wavelengths get larger and loose energy as such ...

4

One small addition to the other answers: While it is indeed true that the light will never stop if it doesn't hit anything, it will however get red shifted, and thus become less energetic, due to the expansion of the universe. For example, the cosmic microwave background consists of photons which were emitted back when the atoms formed. However, back then ...

2

A "ray of light" must be respelled as "photon" because here we are talking physics. Between a single photon and a laser beam, in this case, there is no difference. Every photon will continue his travel until stopped, every single photon is "indistinguible" from others (in the sense that they are no different intrinsecally). The photons of a laser beam are ...

2

A ray of light or a laser beam will not stop until it reaches an obstruction. If there is no obstruction, light will NEVER stop. It has no end.

8

Note that it is correct that a photon can travel an infinite distance in an infinite time, but it can not reach any desired point in the universe. This is caused by the expansion of the universe, which also leads to the fact that we can not receive information outside of the observable universe.

Top 50 recent answers are included