Tagged Questions

Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.

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Is it possible to show that the field of a uniformly moving charge, which is according to Biot-Savart law is given by... $${\bf E}({\bf r},t)=kq\left(\frac{1-v^2/c^2}{(1-v^2 \sin^2 \theta/c^2)^{3/2}}\... 1answer 36 views How are the frequency and wavelength of electromagnetic waves affected within an event horizon? I apologize if this has been asked previously or if my thinking is way off base, but I am inexperienced with relativity (and this is my first question on the site). I am wondering; as one (not ... 0answers 37 views Electron in a Magnetic Field: Force parallel to velocity? According to the four-force given in this question, Force is parallel to velocity. But the Lorentz Force is perpendicular to velocity in a constant magnetic field. Is this a contradiction? [a ... 3answers 90 views Do hot metals radiate? (Thermography) I was looking into thermography which talks about emissivities of metals and other materials. Polished metals which have low emissivity appear to be colder in thermal imaging cameras even if they are ... 2answers 2k views How do you make a spherical radio wave? A vertical rod, a usual dipole, produces radio waves in the horizontal plane, mostly in two opposite directions: If that is possible, how do you produce a spherical EM radiation? should the ... 1answer 66 views How does Compton scattering demonstrate particle over wave behavior? Why is Compton scattering thought to demonstrate light's behavior as a particle over that as a wave. I'm interested in the thoughts at the time of Compton, but also how it contradicts current theory ... 3answers 77 views Why don't E&M fields change orientation after hitting a surface? In essentially every derivation of the Fresnel equations, the general problem of radiation hitting a surface at a certain angle is broken into two parts (out of which we hope the solution any general ... 2answers 35 views What is the player's role in the functioning of a theremin? I recently see a video on how the theremin works, and wasn't satisfied with the answer. I watched around, but they all seem to give the same explanation. A diagram as below is given, and it is ... 1answer 39 views Wave Velocity vs. Phase Velocity I am trying to understand the difference between 'wave velocity' and 'phase velocity'. I know that generally they are equal, but when is that not the case? I, of course, tried to google it, and didn'... 1answer 859 views How can my window not scramble the image of my yard? How can an image pass through a window if the atoms in the glass randomly emit photons in any direction? I've read that glass is transparent because the atoms don't readily adsorb visible light, so it ... 1answer 51 views A single light-wave's ability to divide into two halves? We know from the double-slit experiment conducted "one photon at-a-time" that a light-wave, upon encountering two closely-spaced apertures, is able to split into two halves and travel through both. ... 1answer 54 views How to shield myself from the LTE radiation coming from my phone while working on my Laptop? [closed] I am connecting to the internet with the tethering option on my phone. I wonder if there is a way to shield myself from the LTE radiation (Long-Term Evolution, commonly marketed as 4G) as I am exposed ... 2answers 51 views What exactly are EM waves? [closed] What exactly are EM waves? Wave is just a graph of the intensity of energy at the given point in space right? At a particular point in space, we detect that energy is going up ad then down with each ... 1answer 41 views Frequency dependence of electromagnetic reflection I was surprised to see that the Fresnel equations for reflection depends on refractive index and angle of incidence, but they do not depend on frequency. Why is this case? Are they restricted to ... 3answers 4k views Why do X-rays go through things? I always heard that the smaller the wavelength, the more interactions take place. The sky is blue because the blue light scatters. So why is this not true for X-rays, which go through objects so ... 1answer 54 views Is fire more harmful than a phone? I have read somewhere that the higher the frequency of electromagnetic radiation, the higher the damage it causes to your body, and visible light has a very high frequency in comparison to microwave ... 0answers 14 views Why does a 2-sided propagating EM wave become 1-sided if B is made proportional to E? If you simulate the propagation of an electromagnetic wave in 1D free space (no charges or currents) with initial conditions of E\neq0 and B=0, and you look at a movie of E vs time, then after ... 0answers 31 views Problem with understanding boundary conditions in electromagnetism In some books on electrodynamics they stress that electric current won't radiate if it is placed on a perfect electrical conductor (PEC), citing image theory: exactly opposite current will appear and ... 0answers 94 views How to derive equation for time it takes photons to diffuse through the Sun I am wanting to use the Rosseland radiative heat flux equation to find the time it takes for photons to diffuse through the sun. The answer I am wanting to derive is:$$\tau_D~\frac{\rho \bar C_p R^...
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This question is about Jackson's equation (10.75) and (10.77) I don't know the step in between these two equations.I'm not sure what our unit vector $n'$ will be here and how can we take gradient of ...
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Can 2 photons make up the same colour as another photon?

So, my question deals with the excited electron shown above. (1st diagram) This electron can return to its ground state by either of two ways. One of the ways involves the emission of 2 photons. (2nd ...
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Mie theory: Interpretation in terms of intensity

I'm trying to understand Mie theory. For this I'm reading the book "Absorption and Scattering of Light by Small Particles" by Bohren and Huffman. The derivation of the formulas is fine, but I'm stuck ...
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How much ionizing (carcinogenic) radiation is one exposed to on a commercial flight, what are the sources, and how could exposure be minimized? [closed]

I don't know if this is the best place to ask this question, but I figure a physics-based answer would be the most satisfying. I'd be happy to be convinced I'm being paranoid about protecting an ...
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Detecting position of electrons [duplicate]

To detect particles like electrons, why would the accuracy of the position determined be affected by the wavelength of EM wave used?
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Why the angular distribution of the X-rays from Roentgen tube is not along the decelaration of electrons? [duplicate]

As I understand the X-ray generation from Roentgen tube, is a result from the bremsstralung (and also characteristic lines): from decelerating electrons in the presence of the potential of heavy atoms....
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Definition of a ray?

The typical definition of a ray and the one that I was initially taught was that a ray was a line perpendicular to the wave front. However, when reading up on birefringence it seems as though there ...
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Reflection coefficient of surface with sources

While solving the maxwell equation for surface where both surface charge and current density are present to calculate its reflection coefficient, i.e. $$\nabla \times E=-\frac{\partial}{\partial t}B$$...
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How to find Intensity from field of train of pulses?

Lets say there is process that emits a field $E$ every half cycle of a driving laser pulse (in particular, high harmonic generation). The total field is  E_{tot}(t) = \cdots + E(t-2\pi/\omega)-E(t-\...
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Relation between the electromagnetic wave and quantum wavefunction

I have been thinking about this for a while. I think I misunderstood something about the basics of quantum waves. Let's look at light diffracted in conditions similar to the double slit experiment. ...
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Interference of light waves question

We were recently asked to solve a question in class which goes as follows: In a modified Young's double slit experiment, a monochromatic uniform and parallel light beam of wavelength $6000$ ...
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Intensity of interfering light waves

I had a conceptual question above light wave interference. Suppose that two light beams, each of an irradiance $I$ interfering on an area $A$ of a screen, such that all of the light from each beam ...
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Photoelectric effect on charged plate

As far as I know, to observe the photoelectric effect, one has to expose a metal surface to high-energy radiation. But what happens if the surface has a surplus of electrons? What is the energy needed ...
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Why is glass green?

When I look at a glass block at an angle the edges appear green, but when I look at the edge sideways, so that is directly in front of my eyes it appears transparent. Why?
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Speed of RF waves and IR waves is same as 3 * 10 ^8 m/s?

In space,if we want to measure the speed of RF waves and IR waves it will be roughly 3 * 10^8 m/s ( SPEED OF RF WAVES = SPEED OF IR WAVES = 3* 10^8 M/S ) is this correct ? The different in the ...
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Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?
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Difference between scattering and refraction?

I while back I learnt that when light is incident on a dipole the dipole will scatter the light, and when it is incident on a material of a different refractive index then the light refracts. From the ...
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Is the electromagnetic spectrum bounded somehow? [duplicate]

Is there a maximum frequency that an electromagnetic wave can support?
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Is the photoelectric effect 'Ionising Radiation'?

According to the definition on Wikipedia, ionising radiation is radiation which has sufficient energy to remove an electron from an atom. So a high energy gamma ray is definitely ionising, but visible ...
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Description of a photon and quanta

Could someone please help to clarify the difference between a photon and a quanta? Below is my current understanding - please correct me if I am wrong. A photon - is a 'wave particle' of 'light'. I ...
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Why is everything not transparent? [duplicate]

There is a related question on this site here: Why glass is transparent? Which explains that glass is transparent because the atoms in glass have very large energy differences between energy levels ...
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How can 2 EM waves null each other at a point but continue to propagate?

how can 2 EM waves (travelling in opposite directions) null each other at a point in space but continue to propagate beyond the point in space where they interact to null each other?
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Dependence of Noise Tolerance of waves

Electromagnetic waves are used for transmission of any message. And different kinds of waves have different noise-tolerance. If my guess is right then the noise tolerance is a property of wave which ...
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Why call it a particle and not a wave pulse?

My physics textbook says that photoelectric emission provides conclusive evidence for the particle theory of light. Apparently, since photoelectric emission only works at certain frequencies, we can ...
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Maximum wavelength of a photon/electromagnetic radiation?

This asked; What is the minimum wavelength of electromagnetic radiation? And also this; What is the maximum possible frequency and wavelength? The second question is contradictory; maximum ...
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Why do the edges of glass blocks create a shadow?

I have always observed that the shadow of glass blocks becomes darker as the glass is moved away from the surface where the shadow falls. And I know this is because refracted light rays from the glass ...