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

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172 views

Is it possible to “focus” a radio wave to target an area much smaller than its wavelength?

Recently I was reading about a technology that uses radio waves to stimulate neurons to fire. The radio waves have the advantage of being able to pass through the skull (hence being non-invasive) but ...
1
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0answers
65 views

Hydrogen 2p3/2 -> 1s1/2 transition polarisation and angular distribution

Could you please help me. I have to calculate the intensity angular and polarisation distribution in hydrogen electric dipole transition $\text{2p}_{3/2}\rightarrow \text{1s}_{1/2}$. To do this I ...
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2answers
192 views

Why is the Luminiferous aether theory wrong? [closed]

I saw on this page about the constant speed of light that there are two ways of interpreting this constant speed: General relativity The Luminiferous aether theory I understand why the theory of ...
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1answer
28 views

Wave guide boundary conditions

Why only the normal component of Electric field and the parallel component of Magnetic field exist at the surface of a wave guide or any conductor?
2
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0answers
29 views

Where does the factor of $\gamma^2$ come from in synchrotron radiation?

I've read the derivation for synchrotron radiation (as derived by Griffiths), so I know how to get it given the retarded potentials, etc. I'm having a hard time with intuition. The derivation in ...
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0answers
43 views

The energy of an electron in a time-dependent electric field

Is energy of an electron in a time-dependent electric field any different from the one in a static field? Why did D.Griffith state in his "Intro to QM"( when he discussed the perturbation of EM waves ...
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2answers
75 views

Solution of one dimensional wave equation by variable separation method

When solving the One dimensional wave equation by variable separable method, we equate left-hand side and right-hand side to a constant which is negative in nature. Why has the constant be only ...
3
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1answer
65 views

Electromagnetic radiation bending on Earth

Most articles say that a radiowave is able to propagate itself beyond the horizon because it is reflected off by the ionosphere (and the Earth itself). But do radio waves also get bent according to ...
3
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1answer
105 views

Non-polarised light

We know the beam of light oscillates in electric field and magnetic field, both perpendicular to both the wave of propagation and each other. What does, however, a non-polarised beam of light look ...
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2answers
852 views

Can polarized light be unpolarized again?

I was just wondering if there could be a process that could unpolarize polarazied light. Is that possible?
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2answers
35 views

How are different wavelength components collected by the same detector in a spectrometer?

Let's think, we have a detector array (128x1 and each CMOS detector responds 400 to 1000 nm TSL1401CL that way, each detector has 4.6875 nm interval). Then, basically in a spectrometer a prism reflect ...
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3answers
119 views

Plane waves - EM wave

An accelerating electric charge will emit transverse electromagnetic waves. These waves are propagating away in wave fronts that become flatter and flatter as getting further from the source. So they ...
3
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1answer
88 views

What does a hot, optically thin gas *look* like?

In another question I tried to answer what a sample of the Sun's photosphere or core would look like, if it could be brought into the lab. Here is a broader question - if I have a small inert ...
0
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1answer
68 views

Does reflected light change LED power consumption?

If I enclose an LED in "tin foil" so that the photons it gives off are reflected back to it, would the power consumed by the LED go down?
0
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1answer
43 views

Subtraction In Quadrature?

I have a system of particles (electrons) with an initial RMS energy spread (say "1"). It goes through a section of constant magnetic field (bend magnet) and the electrons radiate. The electrons lose ...
0
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2answers
76 views

Does a rotating DC motor near a TV affects the signals coming in the TV?

In my TV cable the signals were quite noisy so i cut the wire and hanged both the wire parallel to each other. Then the signals became very clear and everything was going alright. Once I was ...
12
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3answers
878 views

What is meant by the temperature of the CMB?

This is what I commonly read: The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the ...
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2answers
62 views

Do I need to convert units to be compatible with constants?

I want to calculate the wavelength of radiation given its energy. I know I need to use $E=h f$ and $f = c / \lambda$. All I'm given is $E = 20 \text{ keV}$, now my true question is: Do I use $E = ...
3
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2answers
52 views

Typical energy of a solar flare

I read that solar flares are customarily viewed in H-alpha light, as a temporary brightening of a small portion of chromosphere. What all can be interpreted from this? Is it because, energy of the ...
2
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2answers
158 views

Are solutions coordinate invariant?

In the case of electromagnetism, we can solve the sorceless wave equation in Cartesian coordinates ($x$,$y$,$z$) getting plane waves as solutions: $$ u(x) = A(x-ct) + B(x+ct) $$ and actually I am not ...
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3answers
355 views

Does light change phase on refraction?

I have seen a lot about when light undergoes a phase change when it is reflected. But does it undergo a phase change when refracted and if so why and if not why not?
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2answers
136 views

Why don't X-rays travel through water?

Why don't X-rays travel through water? I read that X-Rays don't travel through water, but what is the main reason? See this link:http://henke.lbl.gov/optical_constants/ it shows X-ray transmission ...
0
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1answer
69 views

Why is $B=\frac{1}{\omega} k\times E$?

Why can we derrive from $B=\frac{k}{\omega}|E|$ the formula $B=\frac{1}{\omega} k\times E$ ? Obviously, because they are perpendicular, but why is it mathematically legitimate?
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2answers
3k views

How do microwaves heat moisture-free items?

Today I learnt that microwaves heat food by blasting electromagnetic waves through the water molecules found in the food. Does that mean food with 0% moisture (if such a thing exists - dried spices?) ...
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0answers
197 views

Smallest Wavelength of light possible? [duplicate]

I was thinking about blue-shifting of light and I couldn't help my self but think about the limits of blue shifting mechanism and since we know energy of a photon is directly proportional to the ...
10
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0answers
176 views

What is the relationship between Faraday cage mesh size and attenuation of cell phone reception signals?

This is related to the question how can electromagnetic waves reach a cell phone in faraday cage?, where in the answer it was stated that the holes (=size of the mesh) would need to be smaller than ...
0
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1answer
130 views

Stimulated emission direction

Place a sub-micron clump of crystal violet molecules in front of a multipixel detector. Raise the molecules to an electronically excited state with a beam of 590 nm light, illuminating from the side ...
2
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1answer
57 views

Why are laser pulses Sech Squared in temporal shape?

Ultrashort pulses from mode-locked lasers often have a temporal shape which can be described with a squared hyperbolic secant ($\mathrm{sech}^2$) function: $$ P(t)=P_0 \mathrm{sech}^2 \left( ...
0
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1answer
45 views

How did the Huygens probe use EM waves to measure wind speeds on Titan?

In the Wikipedia's article on Huygens spacecraft, it was mentioned that one of the experiments was to measure the wind speeds on Titan by Doppler wind experiment. To quote the exact lines, it was ...
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0answers
84 views

Help understanding Fizeau's calculation of speed of light

While searching for different methods of calculating Speed of light, I came across one of the methods that Fizeau discussed below which I cannot fully understand. In short, in Fizeau’s apparatus, a ...
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0answers
20 views

Why do we assign an electric field vector to an EM wave when photons have zero charge? [duplicate]

In the standard model photons have no charge. So how can en EM wave be given a quantity of electric field to do work on electrons in say a RF antenna. What excites the electrons? I may have parts of ...
0
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0answers
27 views

Ground influence on 434 MHz radio signal

I have read in a paper that ground acts as reflector for radio signals in 434 MHz band. Why is that the case?
11
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3answers
713 views

Electromagnetic waves should stop while encountering a conducting shell?

I am a high school student who has just started reading elementary electromagnetism and am a completely beginner in this subject. I have read in books that EM waves are nothing but sinusoidal ...
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0answers
45 views

How did Rayleigh and Jeans apply the Equipartition of Energy in determining the energy distribution of blackbody - radiation? [duplicate]

I am reading the Ultraviolet Catastrophe and have come across this law. Here , it is written They applied the statistical physics method to the waves by analogy with Maxwell's gas particles using ...
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0answers
45 views

Does the total energy in an electromagnetic field depend on the acceleration of the sources?

If I accelerate a charge from rest to some velocity $\vec v$, does the total final electromagnetic energy contained in the field depend upon the acceleration of the charge?
0
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1answer
478 views

Effect of varying distance of light source from a Light Dependant Resistor

I'm doing the experiment described here and I have a few questions about it. I have a miniature light dependent resistor (LDR) hooked to a multimeter set to $\Omega $ and a $25\,\mathrm W$ Light ...
1
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2answers
202 views

Why doesn't an electromagnetic wave violate conservation of energy?

I'm starting to study electromagnetic waves and as i understand, an electromagnetic wave projects a varying electric field. This electric field can in turn give forces of repulsion/attractions to the ...
0
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1answer
38 views

How does the density of states for black-body radiation change with geometry?

If I have a hollow conducting cylinder with another conducting cylinder inside it (as with a coaxial cable), would the density of states of the photons/radiation between the two cylinders be any ...
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0answers
50 views

Is radar cross section the same as scattering cross section?

There is a quantity known as scattering cross section which is given as a function of frequency. It means the ratio of the scattered power by the particle to the ratio of the incident power on the ...
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4answers
164 views

Why Light isn't like an Acoustic wave?

I just wanted to know why light isn't an Acoustic wave.Is it because light wave doesn't obey acoustic properties?
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0answers
16 views

Tunable ferroelectric material

Is there any tunable ferroelectric (whose permittivity changes by applying electric field) material for visible or near IR applications?
1
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1answer
51 views

Defining photons

I've read every book for my course and all of them describe photons as wave-packets/"bursts" of the EM wave. I just can't appreciate this view of photons. From what I've gathered on photons: Photons ...
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0answers
18 views

Can the granular quantum nature of light be used to engineer a maroscopic optical phenomena?

Today we have optical metamaterials and metasurfaces: materials and surfaces that are made of unit cells with an approximate size of tens of nanometers, that can that interact with light and can have ...
1
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1answer
39 views

How is spectrum controlled? [closed]

I understand that spectrum is considered a national resource for many governments. It is akin to land, water and other resources. It is also a scarce resource. I wonder how is it that government ...
2
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0answers
65 views

What is the relation of scattering, extinction and absorption cross sctions with scattering parameters?

In optics and electromagnetics, they frequently calculate the extinction, scattering or absorption cross sections of a single particle (e.g. a sphere). Scattering cross section which is the ratio of ...
3
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5answers
115 views

Can a Coronal Mass Ejection (CME) cause a blackout on Earth and why?

Can a Coronal Mass Ejection (CME) cause a blackout on Earth and why is it so what's the relation between electro magnetic radiations and electrical and electronic appliance.what exactly does it do to ...
1
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2answers
64 views

Importance of the $\exp (i \bar{k} \cdot \bar{r})$ part of the plane wave equation

I am having trouble grasping how the equation $\bar{E} \left( \bar{r}, t \right) = \bar{E}_{0} \exp \left[ i \left( \bar{k} \cdot \bar{r} - \omega t \right) \right]$ fully describes a plane wave. ...
0
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2answers
49 views

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width?

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width? If I emit an omnidirectional electromagnetic transmission, its power weakens in the ratio of ...
2
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2answers
81 views

Electromagnetism in astrophysics

What is the most important electromagnetic phenomena involved in astrophysics?, I am working in a presentation of magnetars, pulsars and magnetic field of planets and I would like to know if there are ...
1
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1answer
31 views

What happens when an electron and an EMR meets?

The electron on an atom gets excited to a higher level when some how the energy is transferred to the electron. But I can't understand it. I'm no expert of physics. What happens when the electron in ...