Questions tagged [electromagnetic-radiation]
Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
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How can we establish the existence of electromagnetic waves on our own? [closed]
In the realm of scientific inquiry, it becomes crucial to substantiate the existence of phenomena before considering their properties and applications. In the case of electromagnetic waves, the ...
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Speed of EM Waves
We know that for electromagnetic waves, according to Maxwell's Theory
$$v=\frac{1}{\sqrt{\mu\epsilon}}$$
Now consider an opaque object like say Gold. It has a particular value of permittivity and ...
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Microwaves reflecting and making standing waves [closed]
I have a homework problem that I have solved but I would like some extra clarity please.
The way I solved it was, the difference in distance travelled by the top wave (from a peak to 0 amplitude) is ...
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Why is the direction of polarization of EM wave is the direction of Electric field?
The direction of polarization of a transverse wave is defined to be the direction perpendicular to the direction of propagation of wave or the direction of oscillation of wave, right? But in the case ...
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How can things around us have different colours if they have specific emission spectra?
Objects appear in different colours because they absorb some colours (wavelengths) and reflect or transmit other colours. The colours we see are the wavelengths that are reflected or transmitted.
As ...
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Wavelength in Multiple Lossy Layers
I would like to derive an equation for the wavelength of a plane electromagnetic wave (normal incidence) in each layer of a multilayered lossy medium, as shown below.
Which equations are required for ...
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Radiation in an ideal LC circuit
In ceveral textbooks it is said that an ideal LC circuit does not lose its energy, it just bounces from the capacitor to the inductor coil back and forth.
On the other hand, any system where charges ...
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Electric field - when the charge oscillates
If we have an electron moving up and down(oscilating), it produces EM wave.
Let's put charge at (0,0) and it starts oscillating - goes up to 0, 3 and then comes down to 0, -3 and repeating. When it ...
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Derivation of the Eddington limit
The Eddington limit can be shown as:
Momentum of a photon: $ p = E/c = h\nu / c $
Force due to this radiation is change in momentum. Supposedly then,
$$ F_{rad} = \int^\inf_0 \frac{L_\nu}{h\nu}\frac{h\...
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What's the relative phase between current, voltage and electric field in a receiving dipole antenna?
To help keep the question simple, please assume a half wavelength dipole at resonance such as in the image below:
I have been thinking about this problem using the analogy of a harmonic oscillator: ...
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The Classical Theory of Fields: Surface Integral of Poynting Vector Vanishes at Infinity on page 76
I am reading the section Energy density and energy flux in Chapter 4. The Electromagnetic Field Equations of Landau's The Classical Theory of Fields (third revised English edition). On page 76 after ...
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Do electromagnetic antennas transmit (unintentionally scatter) when they receive?
My electromagnetic waves professor said any time an electromagnetic signal is received by an antenna, a transmission also occurs.
I have not independently verified this, but I believe it is likely ...
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Change of light from not visible to visible
Can light from infrared or UV change to visible light when it passes through some other material?
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Electric field - how does it change?
I'm trying to understand why kinks are formed for EM wave.
we got a charge at $x=0$, $y=0$ which has static $E$ field around it. Then, we abruptly move it (only changing its location to $x=0$, $y= -2$)...
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Wireless Power Transfer Modelling
I am trying to develop an analytical model for RF wireless power transfer from an external antenna to an implant antenna, embedded inside layers of lossy tissue.
The external antenna will be ...
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How would we create a device to detect communication using the x-ray and gamma bandwidth? Like a radio. But x-ray gamma spectrum [closed]
I realize the dipole would have to be small enough (in the nucleus of an atom range) and we don't have any mechanism that is small enough to demodulate the frequencies at this rate. But is there some ...
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How do surfaces absorb and reflect light at the atomic level, and what does that have to do with color?
This is sort of a 2 part question that I'm really struggling to figure out.
When white light (which as far as I understand, is just a composition of most electromagnetic frequencies) bounces off, say,...
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Why can a beam of electron and not scatter with a proton to form a H atom? [duplicate]
*Consider aimimg a beam of free electrons towards an isolated free proton . When they scatter, an electron and a protons cannot combine
to produce a H-atom because
A) Energy Conservation B)without ...
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Why not use Bose-Einstein Statistics to derive the Planck's blackbody radiation law?
While deriving the Planck's radiation formula, why do we use MB statistics when we calculate the average energy of oscillators? Shouldn't we use BE?
Is this because temperatures concerned are very ...
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Doubt in the definition of intensity
So I know that radiant intensity is defined as "power transferred per unit solid angle per unit area which is perpendicular to the direction of propagation of energy". So now I have a very ...
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Refractive index of EM waves travelling though a gas of neutral particles
From what I have read and seen online. The explanation of why there is a net reduction in the speed of EM waves through a medium is due to the interference with the oscillating EM fields produced by ...
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What are the light emissions from an ion engine?
Consider an ion thruster like a DS4G (Dual-Stage 4 Grid) thruster. Gas is released, ionized, and accelerated. Assume it's in a vacuum, be it a chamber or space. Also assume the propellant is Xenon.
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Understanding blackbody radiation
I am studying blackbody radiation and modelling a cavity as a blackbody. However, I am encountering a number of confusions in this description:
Many textbooks mention that the cavity consists of ...
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Would dipole antenna work in the following case?
So a dipole antenna is supposed to work with AC supplies.
But would it still produce propagating EM waves if pulses of DC are supplied instead of AC current?
show in the image:
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Can we use a different type of wave instead of light to see elementary particles?
I heard that the visible light rays are too "big" to "hit" the elementary particles (quarks, neutrinos etc) so that they can be reflected. So my question is, would we ...
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What causes the Faraday effect, on a material level?
I understand that the Faraday Effect is due to the velocity of propagation for left and right circularly polarized light being different in many optically-transparent dielectric media when exposed to ...
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What is the physical significance of crest and trough in an electromagnetic wave?
Lets say an electron is vibrating at its mean position. From what I've gathered a crest would be its motion in one direction and a trough would be its motion in another direction. So first of all is ...
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Electric field of dipole antenna
I have seen that the electric field of a dipole antenna detaches and propagates.
For a section of the detached electric field, will the antenna experience recoil if the detached field moves a charged ...
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What are the observable emissions from an ion engine? What percent of input power ends up as heat, UV, or other emissions? [closed]
I'm wondering what would be observable to an astronomer if one knew where to look for a distant space craft with a powerful ion engine, assuming it's detectable at all. I'm doing "back-of-the-...
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Conditions on EM wave complex exponentials and generalizations
The complex exponential ansatz for electromagnetic waves is utilized for algebraic simplicity. However, we admit that, depending on the setup for the ansatz, only the real or imaginary part is of ...
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Compton scattering with free electron
When the photon is incident on free electron, we say that compton happens. Though, we require that photon is x-ray or gamma ray. I wonder why at least x-ray is required.
I have my own observation and ...
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Compton Scattering Notion
I have been reading about Compton Scattering and got confused about exact technicalities. So forgive me if I ask multiple questions, but all related to each other. This is due to the fact that you don'...
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How does inner Bremsstrahlung work?
I'm trying to understand inner Bremsstrahlung. I know this applies to beta minus decay, but have a hard time understanding how it works. In the beta decay, electron is emitted from nucleus. I believe ...
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Why do coloured objects reflect specific wavelength. Is reflection merely transition of electron or oscillation of electron
We all have heard that a coloured object appears so cause it absorbs other wavelengths of white light and reflects or remits (are they different ?) only the a certain wavelength. Recently i read that ...
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How to calculate the change of the density of photons in different frames?
I have a problem in getting the transformation of the intensity of light.
1>> Using the transformation of the energy-momentum tensor $T^{ik}$, we can obtain
We have used the fact that $T^{00}=W$...
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What happen to the electromagnetic waves when a photon's "wave function" collapses?
We interpret the electron's wave function as a probabilistic wave function. During a measurement, it has the probability to collapse to any of the eigenstates of the measurement operator based on the ...
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Refraction of light vs electric field [duplicate]
As we all know light being an EMR has a magnetic and electric field component perpendicular to it. Also when light changes it's medium it gets deviated.
But in electrostatics when we consider electric ...
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What are the underlying concepts of the wavelength? [closed]
For all light waves:
$f = c / \lambda$, where $f$ is the frequency, $\lambda$ is the wavelength, and $c$ is the speed of light.
What are the underlying concepts of the wavelength?
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Do blackbodies emit gravitational waves?
It was previously my understanding that the reason blackbodies only emit light was because light was the only massless particle, so there exist excitations of the electromagnetic field of arbitrarily ...
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Electric and magnetic fields with a phase difference in EM waves
According to Maxwell's equations, electric and magnetic fields (EF and MF) should have the same phase for EM waves.
Also, they must be perpendicular and perpendicular to the propagation direction.
If ...
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Refraction of light vs. electrostatic electric field lines [closed]
As we all know light being an EMR has a magnetic and electric field component perpendicular to it. Also when light changes it's medium it gets deviated.
But in electrostatics when we consider electric ...
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How photon travel diagonally in a spaceship at relativistic speed according to Special Relativity
According special relativity, the clock ticks slower on spaceship moving at relativistic speed because the light travels a longer diagonal distance with respect observer on ground.
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Why no dark lines for black body? [duplicate]
Black body is an object, hence it's made of atoms. Depending on what atom it consists of, that's how the emitted spectrum should be in my opinion. If it contains hydrogen, absorbed light on black body ...
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Why does redshift happen?
If an object B does NOT move away from us, doesn't matter whether it's 10 km or 5,000,000 km away from us, I think redshift wouldn't happen.
Now, if the object is moving away from us, it's said that ...
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Role of "cavities" in quantum light absorption
I am currently studying the basics of Quantum Electrodynamics, and I have learned from this that photons are the quanta of excitation for given field modes. In other words, when a photon is absorbed, ...
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Which linear region should be considered in a Tauc plot when two appear, the one closer to the origin, the one farther away, or both?
I am analyzing the band gap of $\rm TiO_2$ samples made by ALD and titanium anodization. My doubt is that in the samples made by titanium anodization, two linear regions appear in the Tauc plot, and I ...
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Do EM waves carry momentum and if they do can it be used to generate thrust? [duplicate]
I read EM waves carry momentum and can exert pressure, if this is the case can ejecting them be used to generate thrust? Radiation pressure is cited as a real thing but I read about the EM drive and ...
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Density function with Planck's law
I've been looking at all this for the last 2 days and I can't sleep anymore unless I understand it. I think I come to the below conclusion. Much appreciated.
Planck says that the below formula returns ...
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Max Planck - what does 'per wavelength' mean?
Planck says
$$B_\nu(T)=\frac{2hc^2}{λ^5}\,\frac{1}{\mathrm{e}^{hc/λk_BT}-1}.$$
It's defined as energy emitted per unit volume per wavelength. I'm not sure if this includes per solid angle, but I ...
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Max Planck - what's the $B$?
Planck says
$$B_\nu(T)=\frac{2\nu^2}{c^2}\,\frac{h\nu}{\mathrm{e}^{h\nu/k_BT}-1}.$$
It is power emitted per unit area per unit angle per unit frequency. This is what I'm curious now.
Let's say we ...
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