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

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74 views

Confused about SI and CGS Units For E/M Energy

I've been looking at some papers on wakefields of electron beams and I am a little confuded about the units. They do not specify whether or not they are in cgs or SI units. Here is a sample equation: ...
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23 views

Understanding What A Wakefield Describes?

I am trying to understand the some of the properties of wakefields, namely the energy change. So, as a preface I am interested in primarily the wakefield due to electron beams as they progress through ...
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3answers
656 views

Curl of an electromagnetic wave?

I can't understand the concept of the curl of an electromagnetic wave. $$ \nabla \times E = -\frac{\partial \textbf{B}}{\partial t} $$ All of the examples I find show a current through a conductor, ...
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1answer
213 views

Electromagnetic waves in an antenna

There is a few questions that need to be answered in detail but in an easy way... What does it mean to describe the 'plane of polarisation' of electromagnetic waves? Why will some antenna have rods ...
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1answer
21 views

How does intensity differ from apparent luminosity in the context of photometry?

Context: photometry in astronomy. Background: The total luminosity $L$ of a star is the energy that radiates in all spatial directions in all wavelengths and is given by the following formula, where ...
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1answer
62 views

Electromagnetic waves and group velocity

I have three questions about electromagnetic waves and was wondering whether anybody here could comment on these things: Wikipedia says that there are no longitudinal EM waves, although TM and TE ...
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1answer
111 views

Blackbody and standing waves

I'm reading articles about black body radiation and why classical mechanics fails to explain it. My question is: Why do EM waves have to be standing wave in a cavity?
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1answer
250 views

Constructive Interference of Electromagnetic Waves

So I was wondering if Electromagnetic wave has the same property of interference as normal waves. I understand that both the electric and magnetic parts of the wave would have to be in the same ...
2
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1answer
99 views

What does it mean for an electromagnetic structure to be resonant?

There are many electromagnetic structures used in microwave engineering and EM devices. For example, patch antennas, metamaterials made from unit cells, etc. When they design structures like patch ...
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1answer
35 views

Increasing Earth's albedo

How much of a difference would it make if every roof, road and vehicle were painted white? This would certainly reduce the urban heat island effect but how much of a difference would it make to total ...
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1answer
29 views

is it possible to change the energy of a waveform like radio wave & turn it into microwave?

In the electromagnetic spectrum, the differences between all waveforms are the "frequency" & energy of the waveform. We are able to modify both of these parameters. So, is it possible to change ...
5
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1answer
72 views

Question on luminosity of a radiant source and its dependence on temperature, and involvement of Doppler Effect

A few days ago, I happened to go through the chapters on Radiation, and Photometry, studying them at quite an elementary level. I studied Wien's displacement law, and the dependence of luminous flux ...
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5answers
5k views

Can the sun cast a shadow?

The sun's light can cast the shadow of another object, but does it ever cast its own shadow?
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1answer
76 views

Absorption of waves in a plasma

Suppose a plasma has characteristic frequency $\omega_p$. Since $$n = \sqrt{\left(1-\frac{\omega_p^2}{\omega^2}\right)} $$ For $\omega<\omega_p$, the refractive index will be imaginary - which ...
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1answer
50 views

Mathematical Formulation for Accelerating Charges Generating Light?

I haven't been formally taught the fact that accelerating charges generate light, and I have seen the picture of an accelerating charge sending ripples down its field lines, but is there a ...
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4answers
721 views

Why can x-rays pass and not radio waves?

If we stand in an elevator or other metal containers we lose radio signals etc the very same reason for which we cannot see across a block of metal that light cannot penetrate it. However x-rays and ...
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1answer
69 views

Electromagnetic wave in a medium with $\sigma \ne 0$ [closed]

I want to prove that the reflectancy of an Electromagnetic wave in a medium with $\sigma$ $\ne$ 0 is: \begin{align*} R_{\|}=R_{\perp}=\frac{(n-1)^2+k^2}{(n+1)^2+k^2} \end{align*} any advice, please? ...
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0answers
156 views

Can temperature affect or change the wavelength or frequency of EMR?

If we were to emit Electro Magnetic Radiation(X-rays for example) to a very hot body such as the sun would we still get X-rays if we had a capturing device at the other end or would the high ...
6
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3answers
2k views

How is temperature related to color?

I spent some time studying about temperatures and color of objects. It turns out that as we heat something it turns to red, then yellowish white and if we heat it more it turns to bluish-white. Like ...
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1answer
130 views

Visualization of electromagnetic field [duplicate]

In the Wikipedia article about electromagnetic radiation one can find the following picture: But shouldn't the E and B field be 90$^\circ$ out of phase? In the depicted way the energy isn't ...
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0answers
70 views

Diffraction grating zeroth order intensity

I don't understand how the zeroth order intensity maximum works. The intensity of a transmission diffraction grating is: $$I=I_0\sin^2(β/2)/(β/2)^2\sin^2(Nγ/2)/\sin^2(γ/2)$$ Where $γ =kd\sin(θ)$, ...
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1answer
48 views

Signal Induction in a Wire due to Alternating Current

I wanted to make sure I understand induction well enough. Assume we have two wires running parallel to each other. Wire A has a signal of $f(t)$, wire B has a signal of $\hat{f}(t)$. Let's connect a ...
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4answers
678 views

Does Light Experience Length Contraction?

Lorentz length contractions states that the length of any moving object gets divided by the Lorentz factor equal to the Lorentz factor for that object (always $\geq 1$), equal to $$ ...
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0answers
18 views

Redshift Mechanism [duplicate]

How does the stretching/expansion of space cause redshift in light from distant stars? What is the mechanism that causes the electromagnetic crests to be further apart?
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0answers
99 views

EM wave properties [closed]

Here are two small questions about EM wave properties: Question 1: Why do E and B propogate simultaneously? See picture I mean why do not works a paradigm “changing E makes B and changing B makes ...
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2answers
671 views

Interesting relationship between diffraction and Heisenberg's Uncertainty Principle?

I recently came across an interesting explanation of diffraction through an aperture which does not use Huygens' Construction but instead relies on Heisenberg's Uncertainty Principle: The ...
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2answers
218 views

What does an analog voice transmission look like in the visible spectrum?

Analog radio signals are transmitted using light in the radio area of the spectrum. If it was transmitted using the visible spectrum instead (using a visible light emitting device instead of a radio ...
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1answer
81 views

Momentum of Light Question [duplicate]

Since light beams carry momentum, why would a person holding a flashlight not feel a recoil similar to that of a rifle being fired?
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1answer
85 views

Can a single photon induce current in a very small coil?

As I know from Lenz's law, I can induce current in a coil just by changing the magnetic field flux inside the coil. As I know from physics course, photons are electromagnetic waves (so they are the ...
2
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1answer
135 views

Are photons electromagnetic waves, quantum waves, or both? [duplicate]

Are photons electromagnetic waves, quantum waves, or both? If I subdivide an electromagnetic field into smaller electromagnetic fields, should I eventually find an electromagnetic wave of a photon? ...
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1answer
2k views

Intensity of unpolarized light through polarizer

When unpolarized light is polarized with two polarizers, the intensity becomes $I=I_ocos^2(θ)$ (Malus's law). But when unpolarized light is polarized with only one polarizer, the intensity is reduced ...
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3answers
309 views

Is it possible to produce gamma radiaton using radio emitter?

As in the title, I'm wondering is it possible. I think it is possible, because we have powerful enough radiotechniques and gamma radiation are just EM waves, not particles. However I think is ...
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2answers
2k views

From power of a laser beam to electric field amplitude

In my experiment, I use a laser beam with wavelength $\lambda=894 \text{nm}$ for some magnetic resonance experiment. Right now, I'm doing some calculation using Quantum Mechanics, which requires the ...
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2answers
159 views

Do object reflect radio waves? [closed]

Do object reflect radio waves just like light waves? I don't know much about their use but can anyone explain how we use this reflection?
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4answers
330 views

Does the speed of medium affect the path of light?

Let's say I shine a laser from a stationary medium into a moving medium (suppose the water is moving very quickly) perpendicular to the interface and back to a stationary medium like this: (Note: ...
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0answers
79 views

Alternative solar panels

I was doing a bit of thinking recently, when I stumbled on an interesting idea. In a simplified sense, solar cells function by absorbing light and converting it into electrical energy. Since visible ...
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2answers
96 views

Could airport security devices detect differences between printed and written documents?

If airport security scanners of any kind (xray, thermal, whatever else they use) looked at two items: A printed paper textbook The same printed paper textbook into which we have inserted a regular ...
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2answers
2k views

Could airport security possibly distinguish gold and silver coins from other coins?

People usually don't carry pure gold and silver coins in their wallets. If I put some in my wallet, would it be likely that airport security would detect some anomaly with my wallet as compared to ...
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1answer
195 views

What is absorption of an electromagnetic wave?

Can any one explain the absorption/transmission/reflection of electromagnetic waves in the wave form? It is generally said that the atom absorbs/reflects/transmits photon. But can this phenomena be ...
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3answers
300 views

Do ionisation of atoms release photons?

I was reading through my text book about Fluorescence. It said "inside a fluorescent bulb, the mecury atoms collide with each other and with electrons get excited and ionised. During de-excitation, ...
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1answer
41 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 ...
0
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1answer
119 views

speed of the light emitted from a fast moving object [duplicate]

Would not speed of the light emitted from the front of the fast moving object be the speed of light + the speed of the fast moving object?
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2answers
168 views

Is a Perfect/Lossless Mirror possible?

In traditional mirrors, some of the input light is absorbed by atoms in the mirrors surface and are 'lost' as heat, degrading the quality of the reflected image. Could this loss be compensated by an ...
2
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4answers
120 views

Faraday's Law - recursive?

So we know that the EMF is induced by change of flux. The thing that was always confusing me is the following: we start changing the magnetic field which in turn induces electric field which makes ...
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0answers
82 views

Point source approximation

I have a 0.05 mm radius sperical source of Photons, and a 10 mm X 10 mm detector aligned to be orthogonal to their distance vector. Distance is D $\approx$ mm. I want to know how good the point ...
6
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2answers
95 views

Energy in electromagnetic radiation

I learned that power intensity in EM (electromagnetic) radiation is $$ I=\frac12c\varepsilon_0E_0^2 $$ This equation implies that the energy in EM radiation is frequency-independent I also learned ...
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1answer
24 views

Radiative Electric and Manetic field from an accelerating electron

Note: I've started a meta post to discuss this type of question. Yes, it looks like it's straight out of a worksheet from a physics class. That's because it is, and it's also why I posted the answer ...
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1answer
86 views

Why do excited states in $^4$He not decay by photon emission?

Here's a level scheme for the $^4$He nucleus (source; click image to see full size): Notice that all of the confirmed decay modes are by disintegration — emission of a neutron, proton, or deuteron. ...
4
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1answer
96 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?
5
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0answers
56 views

Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity $$ ...