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

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Tranverse electromagnetic waves

TEM waves do not exist in waveguide. Is this the correct explanation- Both curl and divergence of TEM are zero inside the waveguide and because of the boundary conditions (electric field zero at every ...
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2answers
90 views

How exactly does applying the Equipartition Theorem to radiation leads to UV catastrophe?

I'm reading a book by George Gamow, "Thirty years that shook Physics" and have trouble understanding his way of describing the UV catastrophe. In a first part he points out that applying the ...
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1answer
65 views

Electromagnetic interaction physical interpretation

Why do radio waves, X-ray and gamma rays penetrate through matter? Can anyone explain me this in terms of incident energy or wavelength of the photon and the effective cross-section that these photons ...
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3answers
393 views

How could electromagnetic waves propagate through space although they have no electrons?

How could electric fields in these waves propagate through space although in space there's no electrons for the electric field to be formed? is there another type of charged particles that carry the ...
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3answers
315 views

If I turn the light off in a room why does the light instantly disappear? [duplicate]

So today I was asked a question which I found very simple yet I honestly couldn't explain (embarrassingly). One of my mum's friends who knows I'm a scientist asked me "If I turn the light off in a ...
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2answers
54 views

2.4Ghz microwaves have a 12cm wavelength. How do microwave ovens leak radiation, since any gap in the shielding is much smaller than that wavelength?

I've read (I think on wikipedia, but I can't find the reference) that microwave oven leakage is often due to faulty seals on the door. Given that any gap in the door is going to be far smaller than ...
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1answer
92 views

Phase difference between incident plane wave incident on a dipole and radiation fields from dipole

i have an incident plane wave and a dipole, consider that plane wave incident on dipole. at this moment what happens to dipole? We know that after incident of plane wave on dipole, the radiation has ...
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1answer
66 views

How does the electric field pulse propagate during a change in the magnetic vector potential?

The electric field in terms of the electric scalar potential, and the magnetic vector potential is: $E = -\nabla\phi - \frac{\partial A}{\partial t}$, where $A$ is such that $B = \nabla \times A$. ...
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3answers
975 views

What is the physical meaning of retarded time?

Consider this figure Now, when I measure a field produced by the charge $e$ at the point $\mathbf r$, at the time $t=t_1$, it means that the charge sent the signal field at the time $t=t_r$, where ...
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0answers
18 views

Understanding the definition of SAR value?

I am confused over the meaning of SAR values and different standards in its definitions. While checking of website a mobile manufacturer company for a mobile phone, I found this statement The SAR ...
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1answer
104 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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149 views

Radiative transfer equation solution

The solution of the radiative transfer equation for spherical ionized blob : \begin{equation} \frac{dI_{\nu}}{ds} = j_{\nu}-\alpha I_{\nu} \end{equation} and solution is (Ref: ...
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28 views

Tesla Coils - Is there a risk that the discharge can create x-rays?

I've built a Tesla coil that stands about 3 ft tall and uses a spark gap as the interrupter for the primary circuit. Judging by the size of the streamers it's reaching at least a million volts. ...
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0answers
22 views

What would happen to the Earth's atmosphere if all the solar radiation was in the extreme ultraviolet?

According to this, our Earth's atmosphere is completely opaque to radiation with wavelengths less than 100 nm as this radiation has enough energy to ionize the air. Since the surface temperature of ...
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3answers
138 views

Why does $\nabla \to ik$ when you Fourier transform?

I am reading a text that describes the scattering of light by a particle with dielectric constant $\epsilon$ After a bit of maths starting from Maxwell's equations they obtain: $$\nabla (\nabla ...
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1answer
222 views

What causes the light spectrum to appear on oil surface? [duplicate]

I have observed that when petrol or oil leaks, the light spectrum appear on it. What causes light to split into its constituent colours?
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2answers
121 views

Linear vs. quadratic dispersion relation

In wave mechanics the dispersion relation between frequency $\omega$ and wave number $k$ is linear: $$\omega_n=c k_n$$ But in quantum mechanics, based on Schrödinger's equation, one can show that we ...
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1answer
33 views

When is the displacement current equal to conduction current in case of a parallel plate capacitor being charged?

I came across a text - "Whenever a conduction current is oscillating in time, the displacement current is equal to the conduction current in case of parallel plate capacitor." I am not sure what's ...
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35 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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3answers
183 views

How is a photon measured?

If photons transmit the electromagnetic force, which is observable: the photon or the electron? Do we ever directly measure a photon, or do we only measure it's effect on electrons. For example ...
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1answer
105 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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1answer
56 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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2answers
101 views

Angular momentum of light

Can someone explain the classical angular momentum in electromagnetic theory of light? If I shine elliptically polarised em wave on a black disc it rotates. I would like to know how to calculate ...
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4answers
451 views

Exactly how is the constant measured velocity of light deduced from Maxwell's equation?

For electromagnetic radiation the velocity of propagation is $c = 1/\sqrt{\mu_0 \epsilon_0}$. Since both $\mu_0$ and $\epsilon_0$ do not vary in any inertial frame, then $c$ must be constant in any ...
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Main differences between elastodynamic and light scattering when using S-matrix to find bound states

What are the main differences (top 5 if question is too broad), for using the S-matrix to find bound states, between elastodynamic and light scattering? (if it facilitates a higher quality ...
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25 views

What are the advantages of Magnetocardiography?

I am reading the book Bioelectromagnetism by Malmivuo: Difference between the bioelectric and biomagnetic measurements lies in the sensitivity distributions of these methods. Diverse technical ...
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3k views

Real and imaginary parts of dielectric constant vs refractive index?

So for a complex dielectric constant $\epsilon = \epsilon_a + i\epsilon_b$, the wave vector and index of refraction are related to it through $k = \frac{\omega}{c}n$ and $n = \sqrt{\frac{\mu ...
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5answers
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Producing photons with same frequency, different amplitude wave [duplicate]

I don't understand how two photons of the same frequency can have different amplitudes, neither how to produce them. I know that classically the square of the amplitude is proportional to the energy, ...
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1answer
63 views

Reflection of two electromagnetic waves

Can Electromagnetic waves be reflected by another electromagnetic wave without having any physical (transparent or opaque) material (i.e., in free space with one wave having twice the amplitude of the ...
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1answer
979 views

A two-level system absorbs a detuned photon. Where does the extra energy go?

Let's consider simple two-level system with frequency gap of $\omega_0$ between ground and excited state. Now, when we turn on external electromagnetic field with frequency $\omega < \omega_0$, ...
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1answer
161 views

Is every electromagnetic radiation considered “light”?

Somebody mentioned on Freenode chatroom for physics that All Electromagnetic Radiation are delivered in form of Photons not just light. Is it true? Does that mean if we get a THF electrical ...
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11 views

Near field and Nuclear magnetic resonance (NMR)

Why does Nuclear Magnetic Resonance (NMR) physics not concern itself with near field physics? All resonance wavelengths in NMR are much larger than bough sample, pick-up coil and excitation coil. ...
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1answer
41 views

Photons, electomagnetism

I read that photons are carriers of the electromagnetic force (one of the four fundamental forces). So, I would like to know what a photon has to do with, for example, working of a motor or ...
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7answers
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Why is electricity not transmitted wirelessly?

Why is electricity not transmitted wirelessly such that we don't need to span cables on the earth's surface? As in: electricity is transmitted wirelessly from the power plant to the household.
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372 views

Which cyan colored line is produced in the Thomson e/m apparatus?

Related: Which green spectral line(s) are emitted in a Thomson tube? After reading Lisa Lee’s OP on an electron deflection tube, although she had some misunderstandings on its operation, I still ...
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72 views

Why can't de Broglie waves be electromagnetic in nature?

We know that the wavelength of de Broglie waves for a photon is same as that of the wavelength of the electromagnetic radiation that carries this photon. Doesn't this prove that matter waves are em ...
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2answers
42 views

How the polarization of electromagnetic wave is determined?

What help us determine the polarization of electromagnetic wave . Does perpendicular electric and magnetic field determine it or does the direction of propagation ?
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31 views

Question on electromagnetic wave propagation [closed]

how to do part d of this question? i have done part 1 to three but part d is bit confusing.
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670 views

Is there a difference between the speed of light and that of a photon?

As in the title I am curious whether there is a difference between the speed of photon and the speed of light, and if there is what is the cause of such a difference?
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Experimentally diminishing random errors for low wavelength UV observations

Part of the work that I do involves observations of solar low wavelength UV observations, specifically UV-B and UV-A II (up to 340nm). I have noticed that when I observe responses on a CCD or CMOS ...
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0answers
31 views

EM Fields Transmitted from an antenna and photons [duplicate]

What is the relationship between The EM waves (light) and photons in some context i studied light as photons and others as EM fields but how they are related....another questions : what's the name of ...
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54 views

Clarification about Bragg's law explanation

The Wikipedia has this illustration of Bragg's law and then says The two separate waves will arrive at a point with the same phase, and hence undergo constructive interference, if and only if ...
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74 views

How strong must a signal be at the edge of the Solar System to penetrate into the Sytem?

A sort-of follow-up to Are the Voyager probes still sending us a signal ? Still following on the news report referenced in the above question, this report indicates further magnetic surprises at, or ...
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2answers
512 views

Why are EM waves transverse?

I was reading Griffiths' Introduction to Electrodynamics, specifically the section on plane waves. I can see that if we want a transverse wave traveling in the $z$ direction that we are only going to ...
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2answers
170 views

Finding the cosmological redshift of a galaxy in the expanding Universe

Firstly, I understand what the Doppler effect is when it comes to sound or light waves. From everything that I've read, we are told that the universe is constantly expanding since the all the ...
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3answers
43 views

Why radiant heat only travels as infra-red waves and not as other types of em waves like UV rays

Heat is a form of energy and em waves carry energy as momentum of photons. So, I think, radiant heat can travel at any frequency. Please correct me.
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Why does the speed of light $c$ have the value it does?

Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed ...
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2answers
372 views

Who discovered that electromagnetic wave doesn't need a medium?

I have read that physicists in 19 century searching for the aether. They thought that light must have some medium to carry. When did they know that light and other electromagnetic wave doesn't need ...
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60 views

Why is a particular wavelength favored by transmission through a thin film?

A sheet of glass is coated with a $500\text{ nm}$ thick layer of oil ($n=1.42$). For what visible wavelengths of light do the reflected waves interfere a) constructively? b) destructively? ...