# Tag Info

25

The problem with the suggestion of using polarization is that you now have the reflections off the polarizers to contend with. I think the short answer is "it depends on how 'black' you want it to be". "Truly black" = reflectance of 0. I am quite sure that is impossible - there will always be some probability of light scattering off a surface. All you can ...

22

The others have already provided good explanations, but since it sounded like an interesting question and I already sketched up a diagram, I thought I would show it, too. As already mentioned, if you have an object that is to be shown as the exact same distance as the distance between you and the screen, it's very easy to represent that: It's just a single ...

20

See the Wiki article on Polarized 3D glasses. Most likely, you have a pair of circularly polarized glasses. The mirror reverses the circular polarization. The article on Circular polarization does it better than I would be likely to achieve in less than an hour or two. Or Hyperphysics, or Google.

19

I can't improve on KDN's answer, but given Todd's comments this is an attempt to rephrase KDN's answer in layman's terms. A system is only in an eigenstate of spin around an axis if a rotation about the axis doesn't change the system. Take $z$ to be the direction of travel, then for a spin 1 system the $S_z$ = 0 state would be symmetric to a rotation about ...

18

Let's do some math in order not to be unsubstantiated. 1. Perpendicular polarizations. First wave $E_{1x} = E_0\,\cos\omega t$, second wave $E_{2y} = E_0\,\cos(\omega t+\Delta)$. Here $\Delta$ is a phase difference between waves. Total field: $$\vec{E} = E_0\left(\vec{i}\cos\omega t+\vec{j}\cos(\omega t+\Delta)\right).$$ Intensity: $$I_\perp\sim \langle|\... 16 The key idea of how LCDs work is that a peculiar substance, a "liquid crystal", is placed between two linear polarizer filters. The filters are crossed, so normally a backlight behind the LCD isn't seen, appearing black. When voltage is applied to part of the device, such as one segment of a 7-segment digit, or one row and column defining one pixel in an ... 16 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' ... 15 Nothing is happening. At least, nothing except that a new generalized quantity suggestively called "angular momentum" was defined and subsequently measured. But nothing we know about the usual angular momentum of photons is changed by this in any way. Standard total angular momentum is J = L + S, where L is the orbital and S the spin angular momentum. ... 14 Thank you so much for posting this. I had seen this a while ago and never got round to thinking it out in full, and now I have :). Those are not "cheap sunglasses": they are 3D glasses for use with 3D television screens and the like. This is a fantastic demonstration and I encourage anyone with a spare pair of these glasses at home to take them apart to play ... 14 It's the same \ell that indexes the spherical harmonics Y_{\ell m} (or Y_\ell^m if you prefer). We can decompose functions defined on the sphere (like anything defined on the sky) into a countably infinite sum of appropriately weighted spherical harmonics. \ell counts the number of nodes, while different values of m, 0 \leq \lvert m \rvert \leq \... 14 By definition of spin S it is a positive integer number or zero. Not to confuse with the spin projection possible values S_z, which may run from -S to S. 12 Cinema 3D glasses (at least those made by Read-D) are circular polarized. This has the advantage that the polarized light reflected from the screen doesn't depend on the angle between your eye and the screen and so you can move your head around while watching. But when you look in a mirror the rotation direction is reversed on reflection. The shutter ... 12 Magnet NNNNNNN SSSSSSS break into NNNN NNN SSSS SSS and is put together NNNNSSS SSSSNNN 12 The absence of the S_z=0 spin projection is related to masslessness of the photon. Because the photon is massless, it propagates at the speed of light and has no rest-frame time evolution. This removes one of the allowed polarization states that would be present for massive bosons. Solving the eigenvalue problem for the spin operator S gives eigenvalues ... 12 It sounds like your teacher's explanation might have been a little misleading. The reason sound can't be polarised is that it is a longitudinal wave, unlike light which is a transverse wave. (Those links have some animated diagrams that should help to make the difference clear.) "Transverse" means that if a beam of light is coming towards you, the ... 11 It is possible to "block" light based on its polarization in a number of ways. In the situation you are describing, where the light hits a polarizing filter, it is simply absorbed by the filter. The filter does indeed heat up, and in fact if you put your hand near the screen you can usually feel that it is quite warm. It is also possible to have a polarized ... 11 Yes. In fact, light will only interfere with light of the same polarization. If you take a Mach–Zehnder interferometer, for example, and put a polarization rotating optic (a waveplate) in one of the arms, the interference pattern will lose contrast. If the polarization is rotated 90 degrees, the pattern will vanish completely. 11 You might start with understanding Rayleigh scattering, and then plane polarized light interacting with a simple anisotropic molecule before going onto chiral ones. A plane polarized light wave is propagating in the direction given by the right hand rule, so let's say it's electric (E) field is in the \hat{i} direction, the magnetic (B) field in the \... 11 The answers from KDN and John Rennie are right - I'll just try to illustrate how it works: The components of a massless spin 1 field satisfy$$\Box^2 A_{\mu}(x) = 0$$Traditionally we perform the expansion in momentum variables$$ A^{\mu}(x) = \int{\frac{1}{\sqrt{p^0}}A^{\mu}({\bf{p}})e^{-ip.x}}d^3{\bf{p}} + \textrm{c.c.} If the particle is moving in ...

11

For a single photon, the only similar physically meaningful question is whether the circular polarization is left-handed or right-handed. Quantum mechanics may predict the probabilities of these two answers. An experiment, a measurement of L/R, produces one of these answers, too. After the measurement, the photon is either left-handed or right-handed ...

11

Photons, as each massless particles, are characterized not by spin (which is defined as total angular momentum at rest, and mathematically corresponds to irreducible representation of the little group of representation), but by helicity $\lambda$ - the projection of total angular momentum on the direction of motion. Actually, the Casimir operator, which ...

10

The usual way linear polarisation is measured is by shining polarised light onto a polarising filter, rotating that filter and then using Malus' law to fit the data to a $I_0 cos^2(\theta_{beam} - \theta_{polariser})$ shape. By finding the angular position of the intensity peak we can infer the angle of polarisation of the incoming beam. Now, assume we ...

10

Materials, and certainly materials transparent to light , have few magnetic properties. They are not composed out of atoms that have strong ferromagnetism. But all atoms have strong electric fields. This means that light, as it goes through a transparent medium has small probability to interact with its magnetic field component with the medium, which is ...

9

Ernst Mach has once designed an experiment which nicely illustrates linear polarization using a glass cone. Polarized light falls on the cone from the top at Brewster angle. In case of unpolarized light the reflected light has symmetric distribution while with linearly polarized light two dark strips occur in the plane of polarization. It is demonstration ...

9

I generally agree with the above answer. But I can explain the same by simpler words IMHO. Linear polarization may be expressed as a superposition of two opposite circular polarizations. And the polarization direction depends on the phase difference of the two circular polarizations. In simple words: imagine a situation where you add two vectors that rotate ...

9

With any simple harmonic oscillator there are two quantities we are interested in, the phase and the amplitude. Complex numbers are an easy way to represent both of these in a single value, especially as a complex number can be written in the form $Ae^{i\theta}$ where $A$ is the amplitude and $\theta$ is the phase. This doesn't mean light has some "imaginary"...

9

This link: http://alienryderflex.com/polarizer/ has an excellent explanation; much better than anything I could write here. Essentially, it says that this occurs because the 45 degree filter outputs a projection of the vertical rays at 45 degrees. This, in turn, has a horizontal component, which the final filter projects in its output.

9

Malus's law is about the effect of a polariser on polarised light. You've clearly read a badly written version of it. What your author likely meant to say was: One begins with unpolarised light; The first polariser quells the unaligned component of the unpolarised light and outputs polarised light (with half the input's intensity). This polarised output ...

8

Unpolarized light is not a superposition of polarized light (which would again be polarized) but a mixture of polarizations in all directions. It cannot be described by a single solution of the Maxwell equations. Instead one needs for proper modeling the statistical version of electrodynamics. See the book on quantum optics by Mandel and Wolf (its first ...

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