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

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If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
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0answers
19 views

Dipoles in an external rotating field?

Consider a bunch of magnetic dipoles in $x-y$ plane in an external magnetic field $B(t)=B_0 \hat{z}+B_1(\cos\omega t~\hat{x}+\sin\omega t~\hat{y})$. The dipoles are rotating around $z$ axis and of ...
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1answer
62 views

Would neutronium emit heat?

Since accelerating a charge creates EM radiation, and there are no charges in neutrons to be accelerated, would that mean neutronium emits no radiation? Consequently, to preserve the second law of ...
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5answers
2k views

The rule breaker, emissivity + reflectivity = 1

If emissivity and reflectivity are inversely proportionate, why does glass have a high emissivity of around 0.95-0.97 as well as being very reflective for IR Radiation? normally it works but not with ...
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2answers
47 views

How to determine the angular velocity of a particle with mass $m$ and charge $q$ in a constant B field? [on hold]

$\textbf{PROBLEM:}$ A particle with mass $m$ and charge $q$ moves in a constant magnetic field $B$. Show that, if the initial velocity is perpendicular to $B$, the path is circular and the angular ...
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0answers
28 views

How easily can we pick up radio signals from outer space

I've always wondered about the concept of listening to radio signals from space to try and look for alien life - how accurately can we distinguish "man"made radio signals from other forms of radiation ...
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2answers
56 views

How is the virtual image reconstructed from a hologram?

To make a hologram a film is exposed to an incident plane wave and wave from the object to record the interference pattern on the film. The principle is commonly explained in a way like that in p.1212 ...
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2answers
82 views

Can kinetic energy in atoms result in emission of all types of EM radiation?

I already know the fact that when solid objects heat up, they emit thermal energy which is also known as infrared radiation. However, if the atoms in that solid were to begin gaining more or less ...
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5answers
6k views

Why doesn't light kill me?

Why does each individual photon have such a low amount of energy? I am hit by photons all day and I find it amazing that I am not vaporized. Am I simply too physically big for the photons to harm me ...
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2answers
44 views

Why array of telescope is used?

To increase the resolution of an instrument, smaller wavelength and larger aperture is desirable. It is mentioned in some textbooks that the "effective" diameter of a telescope can be increased by ...
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1answer
93 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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1answer
68 views

What's the meaning of linear medium in electromagnetism?

I'm studying the book Polarimetric Radar Imaging: From Basics To Applications and on page 31, there's this sentence: In the following, we shall consider the propagation of an electromagnetic ...
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0answers
30 views

What is ultimate AC frequency and phenomena related to it?

Just as in title. What is the top AC frequency physically possible to obtain? And are there (and if yes, what?) phenomena occuring only at large frequencies? I'm thinking about a metallic wire. I know ...
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0answers
17 views

Question about dark fringe in diffraction

In finding the angle for the mth dark fringe of single slit diffraction using Huygen's principle, they usually split the slit into equal portions. For example, to find the first dark fringe the slit ...
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1answer
112 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
238 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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3answers
145 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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4answers
4k views

Why does change in speed of a wave make it refract?

When a light wave enters a medium with a higher refractive index (e.g. from air to standard glass) and its speed decreases, why does that make it refract/bend? I understand that wavelength decreases ...
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1answer
15 views

Does resonant inductive coupling work in the presence of a strong magnetic field?

Does resonant inductive coupling work in the presence of a strong magnetic field? I am unsure because resonant inductive coupling uses magnetic fields to transmit power wirelessly and a strong ...
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2answers
122 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
146 views

Why is the wave equation so pervasive?

The homogenous wave equation can be expressed in covariant form as $$ \Box^2 \varphi = 0 $$ where $\Box^2$ is the D'Alembert operator and $\varphi$ is some physical field. The acoustic wave ...
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1answer
21 views

Should I observe single/double escape peaks for all energies above 1022 keV

I have already asked a question similar to this, but that question was specifically relating to the case of K-40. I'm going to generalize it to any case My question is to do with the field of gamma ...
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3answers
59 views

Observing a photon during flight

When I was reading about the double-slit experiment in quantum mechanics, everything seems to make sense in terms of the waves and the interference pattern, but if thinking more about this ...
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1answer
59 views

What's really a radiowave

Can you explain what we interpret as an EM wave? In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a ...
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3answers
829 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
526 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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How many X-rays does a light bulb emit?

I read somewhere that most things1 emits all kinds of radiation, just very few of some kinds. So that made me wondering whether there is a formula to calculate how many X-rays an 100W incandescent ...
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1answer
33 views

Reflection of EM waves

In reflection of e m waves at the boundary, to show the reflected magnetic fields we put negative sign in the unit vector, example, if the B is along z direction we put (-k) in he reflected wave, ...
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2answers
291 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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1answer
76 views

Physical meaning of wavelength of an EM wave

What is the physical meaning of the wavelength of light? This question has been asked before but I cannot find a satisfactory answer. Some respondents have said that the question is vague, I don't ...
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1answer
87 views

An object glows red at around 1000K while a red star is around 3000K. What causes this misalignment in spectra?

According to the H-R diagram, a red star is 3000K, a yellow star is 6000K and a white star 10000K. But a hot metal appears red at 1000K, yellow at 1500K and white at 2000K.(approximately) Why is ...
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1answer
75 views

Is the photon's wave function the same as an electromagnetic wave(light)? [duplicate]

The first that i have been taught in Quantum Mechanics is the photoelectric phenomenon. Without analyzing it, it concludes that when we shine light at the circuit(roughly speaking), the work required ...
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2answers
75 views

Has someone measured that in the far field of radio waves, the electric and magnetic field oscillate synchronously?

That in near field both fields oscillating 90° displaced is obvious since in antenna rod a lot of electrons will be accelerated and and this oscillation of electric field is escorted by alignment of ...
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3answers
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In electromagnetic radiation, how do electrons actually “move”?

I've always pictured EM radiation as a wave, in common drawings of radiation you would see it as a wave beam and that had clouded my understanding recently. Illustration on the simplest level: ...
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2answers
84 views

Electromagnetic wave and quantum mechanics [duplicate]

I'm very new to physics. I studied and read about quantum mechanics and what the assumptions are (wave particle duality, uncertainty principle, observation, wave function collapse, etc.), but I also ...
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2answers
131 views

Far Field Diffraction of EM waves: what does the zero frequency signify?

If you have a system of independently radiating electrons/point-charges, the far field distribution of the EM waves can be approximated by the fraunhoffer diffraction integral, or simply by the ...
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1answer
50 views

Why does friction produce heat?

What causes two objects sliding against each other to produce heat? Why don't they generate visible light or something else?
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1answer
66 views

Can I produce radio waves by waving my hand?

I learned that EM waves are caused by the movement of charges (e.g. electrons), because they have an electric field and the change in the particle's position doesn't update the field instantly all ...
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2answers
100 views

What is the amplitude of a (EM) wave?

Amplitude is: Peak-to-peak amplitude is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). With appropriate circuitry, peak-to-peak ...
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3answers
114 views

Why photons reflect off glass?

Why photon reflects and refracts through glass? Some photons pass through glass and some reflects.I know this is due to energy levels of electrons of glass, an incoming photon is unable to excite the ...
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3answers
84 views

What is an EM wave? [closed]

How does an EM wave carry energy? What is an EM wave? (Is it a collection of photons?) What are the mechanics behind it? I am an engineer and I've been taught to think of light (light is my area ...
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1answer
118 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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2answers
126 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
100 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
25 views

Transmission of light, sub-wavelength apertures, and cut-off frequencies

I was hoping someone could please explain how the transmission of light through a sub-wavelength aperture in a metal film, at a particular wavelength, changes when the aperture is: i) above cut-off ...
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1answer
49 views

Will I sunburn faster when driving compared to being parked?

I'm not sure if the same logic applies to light and rain when comparing running/driving with a stagnant situation. See, e.g. Why does driving faster make my windshield catch more rain? Suppose I have ...
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1answer
56 views

Question about lens maker's formula

I am trying to follow the derivation of lens maker's formula from the textbook "University Physics", p.1133 ...
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1answer
72 views

Can photons accelerate? [duplicate]

I was just wondering if there's a (hypothetical) situation where a photon could accelerate and what the consequences of this might be?
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1answer
938 views

Power radiated by the Sun at different locations [closed]

I am wondering can someone help to solve second part which extends first part; The power radiated by the Sun is ${3.9*10^{26}}_{watt}$. The earth orbits the sun in a nearly circular orbit of radius ...
4
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0answers
101 views

The logarithmic decay of WIFI

I have been told that Wi-Fi, LTE etc signal strength fall of as $$\propto \frac1{\log(r)}$$ where $r$ is the distance. I am wondering why this is. I better explain what I mean with this question. ...