# Tag Info

9

This is what you seem to be imagining as happening: Whereas this is more accurately what's happening:

5

The photons are not radiated only in perpendicular (normal) direction from the star surface. In fact, they are radiated into all available directions (180 degrees) from every point on a star surface. The same applies for galaxies as well. For this reason there are photons sent into all directions (including the Earth direction) from each point of a star / ...

3

There isn't a straight answer to this question, which sheds light onto the meaning of the subtle word coherence, because what we tend to call "decoherence" can have two main roots. A practical experimental meaning of the word coherence is "ability to show interference", and there are two ways whereby observable interference can disappear: (1) (energy) ...

2

The diagrams that typically figure in textbooks and pop-sci books have the transverse scale massively exaggerated. The slits for a optical wavelength version of the experiment are typically less than a millimeter apart and on order of a tenth of a millimeter or less in width. This means that they are separated by less than the natural width of the incident ...

2

Okay, so: Unfortunately, the word "mass" has been used in two different ways in physics. One was the way Einstein used it in E=mc^2, where mass is really just the same thing as energy (E) but measured in different units. This is the same "m" that you multiply velocity by to find momentum (p), and thus is sometimes called the inertial mass. It's also the ...

2

This shows a schematic illustration of the Pound-Rebka experiment: At the bottom we have $^{57}$Fe source that emits gamma rays upwards with an energy of 14.4 keV. The frequency of the gamma ray is $3.48 \times 10^{18}$ Hz, but let's just call this $\nu_0$ to avoid messing around with figures. The gamma ray travels upwards, and as it travels it is red ...

1

In principle any acceleration of an electron causes some radiation, and an electron has to accelerate in order to leak from one plate to the other. However: the velocities, and therefore the accelerations, of electrons in electrical circuits are small. Calculating the electron drift velocity is an exercise routinely given to students and the results tend ...

1

So, lets step back a bit. First lets look at avalanche breakdown. Electrons are constantly scattering, off atoms and other electrons, with some average scattering rate under given conditions. In a semiconductor, avalanche breakdown occurs when the field is strong enough that a free conduction electron gains (through accelerating in the field) a threshold ...

1

I don't know about sources that emit polarization-entangled photon pairs, but polarization-entangled pairs can be obtained from a polarized source in many ways. One example is Spontaneous Parametric Down Conversion (SPDC). Quoting from Wikipedia: In a commonly used SPDC apparatus design, a strong laser beam, termed the "pump" beam, is directed at a BBO ...

1

I will address: My question - Does not photon, which is supposed to be quantum of electro-magnetic field, interact with an electron "electromagnetically"? A photon and an electron are elementary particles, quantum mecanical entities. Probabilities of interaction in quantum mechanics are calculated from the wave functions of the system in QED, using ...

1

Your reasoning is quite correct, and you can see exactly this phenomenon in a photomultiplier tube. The photomutiplier tube uses very thin metal sheets, and when a photon strikes the sheet the primary photoelectron is emitted in the same direction as the incident photon and escapes from the far side of the sheet: The quantum yield for this process is ...

1

In the experiments for photoelectric emission, the light is incident on one face of the emitting plate, for example the anode, when determining the stopping potential. The electrons are emitted by this face of the plate. Why are the electrons emitted in the direction of the incident light, and not opposite to it? In this answer the energy momentum balance ...

1

Assuming that with "oscillation of the wave function" you mean that the state evolves in time with a relative phase $E/\hbar$ as $\alpha\lvert 1 \rangle +\mathrm{e}^{\mathrm{i}E/\hbar t}\lvert 2 \rangle$, that's really an "accident" because given an energy, how else are you going to get a frequency in quantum mechanics out of it if not by dividing by $\hbar$?...

1

The speed of light is always 299,792,458 meters per second, regardless of the speed of the source and the speed of the receiver. According to Newton's corpuscular theory, both speeds of the source and the receivers were being added or subtracted from $c$. According to an aether theory of the electromagnetic field, the speed only depended on the speed of the ...

1

The speed of light is the same in all frames. If you are moving relative to Earth at 99% the speed of light and you measure the speed of light you find that the speed of light is the same. Assume you shine light in the direction of your motion. From the perspective of an observer on Earth the photons creep forwards at 1% c relative to your frame. However ...

Only top voted, non community-wiki answers of a minimum length are eligible