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

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1answer
27 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
24 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
45 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 ...
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0answers
23 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?
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3answers
600 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
40 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
35 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?
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0answers
27 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 regarding it. I've taken a mini-LDR hooked to a multimeter set to $\Omega $ and a $25\,\mathrm W$ Light Bulb to plot the following ...
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1answer
113 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
22 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
21 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
119 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
10 views

Tunable ferroelectric material

Is there any tunable ferroelectric (whose permittivity changes by applying electric field) material for visible or near IR applications?
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1answer
42 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
17 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 ...
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1answer
31 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 ...
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0answers
37 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 ...
2
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5answers
62 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 ...
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2answers
51 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. ...
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2answers
37 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
53 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
24 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 ...
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5answers
125 views

What exactly are light waves?

We know a sound wave is a disturbance that moves through a medium when particles of the medium set neighboring particles in motion. And using the pressure variations we can plot a pressure/time graph ...
0
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1answer
30 views

What's the relationship between input power and intensity / frequency of radiated EM waves?

I've seen an example of an electric dipole that radiates power proportional to $\ \omega^{4} $. My question is: given a fixed amount of input power to drive the dipole, while varying the driving ...
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0answers
21 views

Atmospheric refraction approximation

I am studying atmospheric refraction, reading ITU P.834 Effects of tropospheric refraction on radiowave propagation, and I have a question about an approximation. They say that refraction correction, ...
0
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1answer
27 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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0answers
12 views

Reaction force due to the curvature and gradient drift

We know that a charged particle will have a drift velocity in both a curved magnetic field and when there is a transverse spatial gradient in the magnitude of the magnetic field. This drift velocity ...
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1answer
45 views

General solution to the wave equation of electromagnetic field

Suppose that we have the four-vector potential of the electromagnetic field, $$A^i$$ The wave equation is given by $$\Box A^i=\frac {\partial^2}{\partial x^k \partial x_k } A^i= \left(\frac {1}{c^2} ...
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0answers
23 views

When optically pumping a lasing gain medium with another laser, does Stimulated, or Spontaneous emission dominate?

Much of my reading seems to indicate that laser pumping results in a fluorescent stokes shift but somehow photon vector is maintained. I've seen the phrase "Spontaneous Fluorescence by Stimulated ...
7
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1answer
140 views

Can light gravitationally affect itself?

Consider a electromagnetic wave in a vacuum. From my understanding of general relativity, The wave has momentum, and thus generates a gravitational field in all directions. The gravitational field ...
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2answers
61 views

What is energy of light, as we know speed of light?

1.What is total energy of EM waves, as all got same speed? If two em waves has same energy, do they have same mass? If same mass and energy, do they have same frequency or wavelength still ...
2
votes
1answer
36 views

Single photon pulse and its electromagnet field

I describe the temporal distribution of a single photon pulse in an interferometer experiment in vacuum via the Gaussian function $\psi$: $$ \psi(t) = \tfrac{1}{(2\pi\sigma^2)^{1/4}} \text ...
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0answers
16 views

What is the effect of alpha particle on a diamagnetic substance?

Can alpha particles induce static charge on diamagnetic substances or temporarily magnetize when they are bombarded on them ? If yes then for how much of time the charge remains on it ? Till what ...
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4answers
565 views

Why is an opaque body opaque?

When does a body qualify to be called an opaque body? Is it anybody which cannot let visible light through it or is there any other definition? And when and how does a body allow radiations through ...
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0answers
28 views

How to represent a laser pulse in quantum optics

Every quantum optics textbook that I've found says something like "a coherent state represents the output of a laser", but a coherent state is a static thing (aside from the oscillating phase of the ...
0
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1answer
29 views

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 ...
0
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1answer
14 views

Chaff-RF Relationship?

What is the relationship between chaff length and the frequency it is meant to interfere with? I've read that specific lengths of chaff are more effective as a countermeasure for specific ...
2
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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 ...
5
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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 ...
0
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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 ...
2
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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 $B = \nabla \times A$. ...
0
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1answer
43 views

How does Huygens Principle explain interference?

How exactly does Huygens theory about the propagation of wavefronts account for interference?
1
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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 ...
0
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1answer
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 ...
2
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2answers
53 views

Negative frequency contributions for very short pulses?

I am wondering if very short optical light pulses can have a Gaussian envelope? When I describe the pulse shape with a Gaussian than the frequency distribution has also a Gaussian shape. But if the ...
1
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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?
3
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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 ...
2
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0answers
11 views

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 ...