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

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How to understand that the electromagnetic wave propagates?

Don't the electric field and magnetic field have infinite range? When a charged particle moves, the electric field vectors at two different locations A and B should start to change at exactly the same ...
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1answer
34 views

Current Electricity

If $$ \frac{dQ}{dt} = I $$ and if an accelerated current produces E.M. waves (radiation), does that mean $d^2Q/dt^2$ (second derivative of a charge w.r.t. time) will give me the magnitude of the wave ...
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16 views

Correct terminology for when neutral atom is ionized due to an electric field?

An electric field will cause an induced dipole in neutral atoms when present - I presume that if the field were strong enough the magnitude of the polarization could exceed a critical length and cause ...
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8 views

Show that the electric dipole term vanishes for a particular current

I'm interested to show that given a ring with radius a where there's a current $I_0 \cos \omega t$ ($I_0$ is a constant) there is no radiation due to the electric dipole term (appearing in the ...
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3answers
52 views

Question about intensity of EM waves

For electromagnetic wave if it's reflected from a perfect conductor standing wave can be form. I wonder why Poynting vector can be used to describe the intensity of standing EM wave. (see p.19 of ...
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3k views

Wavelength-dependent refractive index

I read in a book about optical fibers that the different spectral components of a light pulse transmitted in the fiber propagate with different velocities due to a wavelength dependent refractive ...
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19 views

Counting modes Rayleigh-Jeans

In the derivation of the Rayleigh-Jeans Law, we count the number of EM modes in a square cavity. After calculating the number of allowed modes due to boundary conditions, we multiply it by a factor of ...
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69 views

What maximum theoretical speed can reach spaceship with EM Drive in space? [on hold]

There are several studies (by Institute of Aerospace Engineering, Technische Universität Dresden and by NASA) that are concluding that the EM Drive produces thrust. So I am wondering: if the EM Drive ...
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2answers
114 views

What is fundamentally happening that causes light to change its orientation when repeatedly polarized? (edited)

When light is passed through two polarizers successively, its intensity and orientation afterwards depends on the angle between the polarizers and the orientation of the most recent polarizer, ...
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Absorption of Ultraviolet rays vs. Absorption of Infrared rays [closed]

How does the effect produced by absorption of UV rays differ from that produced by IR?I read that UV undergoes electronic absorption whereas IR undergoes vibrational absorption. Does this mean that IR ...
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1answer
47 views

What is the mix of ordinary mass vs. ordinary radiating energy in the universe?

I have seen data showing that the estimated mix of dark energy in the universe is 68.3%, the mix of dark matter is 26.8% and the mix of ordinary matter is 4.9%1. However, within "ordinary matter," ...
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2answers
652 views

Could an oscillator at a high enough frequency produce light instead of radio waves?

Considering that light is in the 400-800 THz range, if you had an electrical oscillator that ran at that frequency connected to an aerial of some sort, would the antenna emit visible light, in the ...
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1answer
84 views

What is a wavelength of an EM wave physically?

This might be a silly question given I am a physics undergrad, but I was suddenly confused. Usually when EM hit a gap they diffract through the gap. But if the gap is too small, diffraction can't take ...
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41 views

What is the strength of the magnetic field required to penetrate an average human body?

Introduction Suppose you are an experimental nanobot researcher trial-ling a new form of medication that involves activation and control of nanobots within the cells of the interior of the human body ...
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1answer
131 views

Probability density of detection of collinearly emitted photons in two detectors

Update: As proposed by @dmckee, I added equation numbers and improved the display of some equations. The answer by @Trimok inspired me to look at coordinate systems which are not specific to the ...
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0answers
26 views

mixing colour of light

I have seen blue and yellow colours mix to form a light green shade. How can we explain this phenomenon, both in case of light and physical substances like paint ?
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2answers
45 views

will osmium or lead stop all high-energy photons in a shorter distance?

I remember seeing a similar question to this one on Physics StackExchange once. Most of the answers were to the effect of "I don't like the way this question is phrased, so I will insult your ...
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2answers
143 views

Why particles don't lose mass when they radiate

Charged particles radiate when accelerated: in the rest frame of the particle moving with acceleration $\textbf{a}$ the amount $dW$ of radiated energy over time $dt$ is $$ dW \propto \textbf{a}^2 ...
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1answer
80 views

polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its Electric field of wave is perpendicular to earths magnetic field. Now, i read that as it will enter plasma, the wave will ...
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How to model radio wave attenuation by seawater?

From the very limited literature I can find regarding radio waves in saline-water solutions (as in seawater), I have been able to find very few corroborating models of radio wave propagation through ...
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1answer
32 views

Can light (electromagnetic radiation) cause electromagnetic induction in a wire?

Can light, as an electromagnetic wave, cause electromagnetic induction in a wire by passing near the wire? Does a moving electromagnetic wave cause a varying magnetic field in the region near the ...
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5answers
2k views

Can a photon get emitted without a receiver?

It is generally agreed upon that electromagnetic waves from an emitter does not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non ...
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3answers
947 views

why dosen't a charged particle radiate energy in circular motion in a uniform magnetic field?

I have studied in my Physics course that one of the drawbacks of Rutherford's atomic model was that when an electron will revolve around the nucleus, it is undergoing acceleration and so it should ...
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1answer
41 views

What color does graphene glow when heated?

If you heat graphene hot enough, what color would it glow? Is the color within the visible range?
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21 views

Wideband metamaterials in mobile-telecommunications bands

Were there any metamaterials (materials, settings, geometry) studied that are non-resonant (not frequency selective) in the frequencies between 700 MHz and 2700 MHz, therefore useful for mobile ...
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1answer
491 views

Do human bodies give off a consistent but unique radiation/electromagnetic/energy signature?

Is there any facet of the energy emitted by a human body that is consistent and unique - like a fingerprint, but a signal that could be detected by a remote device?
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2answers
37 views

Do all the electromagnetic radiations have dual nature i.e. particle nature & wave nature?

I have studied the dual nature of the light as particle nature & wave nature. A photon of light energy can knock a single electron out of certain metals (usually having less ...
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2answers
115 views

Momentum around an accelerated electron

Assume that an electron is accelerated along the +x-axis. The electron will radiate electromagnetic energy and momentum in every direction. But it seems to me that the EM momentum it radiates in ...
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1answer
220 views

Reaction-at-a-distance: Do charged plates immediately repel each other?

Imagine that we have a pair of parallel plates, $A$ and $B$, separated by some distance as in Fig. $1$ above. At time $t_1$ we simultaneously charge both the plates. This could be done by ...
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1answer
26 views

Layer of graphene on reflector of an antenna

First of all I have no idea how well graphene "sticks" to other metals, but let's suppose it does (well, if I may please ask you to reply to the "stick" question too...). Given the material great ...
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2answers
256 views

Is it really possible to “discover” the speed of light with a microwave oven?

I've seen a number of sites/videos online that describe a method for measuring the speed of light, using a microwave oven and a chocolate bar. For example, this video on youtube. The basic idea is to ...
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0answers
9 views

What is difference between Irradiation & Radiosity?

I have a question in Radiometry: What is difference between "Irradiation" & "Radiosity" in Radiometry? Assumption: the emission & the reflection are specular. I know these physical ...
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2answers
52 views

Wave frequencies and barrier width?

I know a fact that says a wave can go through barriers thinner than its length. This is why for example FM radio can be picked anywhere while antenna TV needs direct sight to the transmitter. Is this ...
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0answers
22 views

Why are most antennas in cellular networks +/- 45° polarized?

I've just been asked a strange question that I cannot find an answer to (even on the internet it seems I can't find any explanation for this) and I ended up wondering why most of the antennas which ...
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5answers
330 views

Can light travel slower than the maximum?

First of all, I know that light does indeed travel slower in a medium like air or water, but that's because the photons are bouncing off of the medium's particles and in different directions so the ...
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1answer
64 views

What does a light wave look like (3d model)

What does a light wave look like? The only models I can seem to find online are 2D waves, they just look like sin() graphs. I have seen the models of the two components of "light waves" (electric ...
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1answer
101 views

Is the wobbly rope depiction of a radio wave inherently wrong? And how do vectors of parallel waves align with each other?

I don't have a scientific education, yet I'm scientifically curious. Among other things, I'm struggling to understand the nature of electromagnetic waves. What I have recently realized is that the ...
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1answer
27 views

Is there a limit to how thin EM radiation can be spread out?

Sorry if this is completely off base but from my understanding, electromagnetic radiation, such as light, becomes less intense the further away it gets from the source. I assume the reduction of ...
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3answers
134 views

Why diffraction is related to wavelength not amplitude

For diffraction, the wavelength of the incident beam should be in range magnitude of the slit length, but why the amplitude is not related to the length of the slit?
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1answer
39 views

Do electrons emit radiation due to gravity [duplicate]

Do electrons accelerating in the presence of a gravitational field radiate due to this acceleration?
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1answer
38 views

$\sqrt{\frac{\omega ^2}{c^2}-k_z^2}$ in cylindrical harmonics

The radial component of the solution of the wave equation in cylindrical coordinates is $$J_\nu \bigg(\rho\sqrt{\frac{\omega ^2}{c^2}-k_z^2}\,\,\bigg).$$ But I always thought that $\frac \omega c$ ...
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0answers
42 views

How can electric and magnetic fields have any component in the direction of propagation of electromagnetic waves?

In case of waveguides we talk about $E$ and $H$ having non zero component in the direction of propagation of wave. But the entire basis of EMW is that $E$ and $H$ are perpendicular to the direction of ...
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1answer
112 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
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4answers
768 views

Electromagnetic wave reflection vs. light reflection

Related: x-ray interaction with atmosphere I know that electromagnetic waves of particular frequencies reflect from the ionosphere. And the light (which from one perspective is an electromagnetic ...
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2answers
38 views

Classical absorption of radiation

How does electromagnetic radiation get absorbed by an object (like a black body) in the classical regime? In the classical picture, electromagnetic radiation is produced by the movement of charges, ...
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1answer
85 views

Can electromagnetic fields be used to deconstruct and reconstruct molecular bonds?

I was thinking one day and came up with a theory after reading about how scientists were studying anti-matter by using electro magnetic fields to separate matter from the anti-matter they made. It got ...
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1answer
36 views

Light / TEM wave in a hollow waveguide

I'm cramming for my EMF exam, and a question came up: Light in free space is an example for a TEM wave, isn't it? (Maybe thats already my mistake) And we learned that in a hollow waveguide only TE ...
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2answers
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“X-rays”, “gamma rays”, “sun rays”… But electromagnetic waves are NOT rays and DO NOT consist of rays?

In a separate question I'm struggling to figure out the nature of EM waves. But it's a vast topic and I'm trying to narrow it down to small specific questions. It turns out that all electromagnetic ...
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5answers
1k views

How do EM waves propagate?

I have read about this and what I surmise is that when charged particles such as electrons accelerate they produce time-varying electric fields. These E-fields produce H-fields and the process goes ...
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3answers
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2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...