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

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### Question about unit for intensity

The picture is from one physics textbook about treating sun as a blackbody and compare the electromagnetic radiation spectrum. Note the unit used for Intensity in the picture shown, it's Watts / (...
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### Why are there hemispheres in Huygens principle?

In the formulation of Huygens principle, it is said that the secondary waves are spheres but on the plots for determination of the wavefront there suddenly become hemispheres? What is the reason for ...
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779 views

### Is laser light a standing wave?

If I understand it correctly the light waves are standing within the laser cavity as they bounce off the walls. Does that mean they remain standing as they leave the cavity? There is nothing out there ...
• 1,537
506 views

### Refractive index of water

The index of refraction is given by the following formula: $$n = \sqrt{\frac{\epsilon \mu}{\epsilon_0 \mu_0}} = \sqrt{\epsilon_r \mu_r},$$ where $\epsilon_r$ is the relative permittivity/dielectric ...
• 271
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### 1-Dimensional Frequency Density Diagram along axis $n$ and distance?

I was reading Resnick and Eiseberg's Quantum Mechanics in conjuction to watching this video on the UV catastrophe : https://www.youtube.com/watch?v=rCfPQLVzus4&t=1206s&ab_channel=...
1 vote
207 views

### Are electric field lines always perpendicular to a conductor's surface?

I know that in a conductor body, in an electrostatic situation (Where $\vec E=0$ in the interior), the E field must be perpendicular to the surface outside because it is solely generated by electric ... 79 views

### Why is the electric field on the surface of a perfect conductor zero when an electromagnetic wave hits it? [duplicate]

I am studying electromagnetic waves, and in many texts it is stated that when a plane wave hits the surface of a perfect conductor, the electric field must be zero in the surface and inside the body. ... 79 views

### Microwave interference inside a leaking Faraday Cage

Let's consider a perfect cubic Faraday-cage with solid metal walls of several centimeters' thickness. Radio waves from the microwave region are fully blocked by this cage, and the fieldstrength inside ...
35 views

### Excitation and acceleration of charges is the only way to produce EM radiation?

In lasers electrons are excited, in free-electron lasers electrons are periodically accelerated as well as in radio antennas. Radiation is produced when deflected in a magnetic field. Thermal ...
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### Virtual photons and slowing down longitudinal wave propagation

It is often described, that virtual photons are mere mathematical constructs, that can turn to real photons if there is enough time and space. And also, that virtual photons can mediate longitudinal ...
15 views

### Book recommendation on interference with relativistic treatment

I'm looking for a book that treats the propagation of EM waves in a medium with an index of refraction $n(x)$, with the idea of looking for the interference caused by two light rays that travel along ...
1 vote
48 views

### Is the concept of the emission of photons applicable to radio waves? [duplicate]

I know that the emission of photons occurs when electrons are accelerated or deflected. Since electrons are also accelerated in antenna rods, the concept of photon emission should also be applicable ...
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43 views

### X-rays during the generation of long-wave radiation [closed]

When generating long-wave radio radiation, do not stand next to the antenna mast, as X-rays are present here. The same applies to radars, which also generate X-rays. How is this unwanted radiation ...
• 9,283
1 vote
39 views

### Why does the area close to a charged particle move at the exact speed as the particle itself? [closed]

when a charged particle moves the area around it moves at the same speed as the particle itself so if the particle had a velocity of 10m/s down then the electric waves at a 10m radius around it moves ...
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51 views

### How many alpha and gamma rays are given off from nuclear waste uranium 235

From the products of uranium 235 waste how much total energy / beta, alpha, gamma rays would be emitted from the decay of uranium 235 over its time of decay.
1 vote
46 views

### $Q$ Transfer via Radiation Formula

According to the formula: $$\frac{\Delta Q}{\Delta t}=\sigma\epsilon A T^4$$ What does $T$ refer to in a situation where I am modelling the power of radiation from air of temperature to surface of ...
• 113
3k views

### Why does high frequency have high energy?

The electromagnetic spectrum's wavelengths all travel at the same speed, $c$. Also, the wavelength $\lambda$ and frequency $\nu$ are related by $c = \lambda \cdot \nu$. Since all moving particles here ...
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3k views

Does a radio receiver "collapse" a wave function when listening to a radio broadcast generated via a transmitting antenna? Background: There has been much discussion on this forum (here) ...
• 279
2k views

### Do all objects at the same temperature glow the same color?

Does Kirchhoff's law for heat radiation imply that all objects at the same temperature will glow the same color? In other words, if a piece of molten iron glows the same color as my body, which ...
• 537
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### What does the electromagnetic wave of a photon do?

So for example in the double slit experiment, you can see the interference pattern on they screen of where the photons hit it. That makes sense to me. What doesn’t is that since in this simulation, if ...
• 103
127 views

### Right hand and left hand orientation for electromagnetic waves

An EM wave has an electric and a magnetic field component and in a vacuum both are perpendicular to each other. As you can see from the Wikipedia sketches and my scribbles, the waves in the pictures ...
• 9,283
1 vote
34 views

### How does a scintillator work? [duplicate]

I am trying to understand how a scintillator works. Currently my understanding is this: gamma radiation interacts with atom A (through photoelectric absorption or compton scatter) which produces a ...
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### Penetration of electromagnetic waves in insulators?

The exact formula for the attenuation of E&M waves in a conducting material can easily be found in most textbooks on applied E&M. I am wondering if such a equation (approximation or not) ...
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70 views

### Why there can't be an isotropic radiator?

Why there can't be an isotropic radiator? I know you can prove it using Maxwell's equations but I don't see how. Can someone please help?
1 vote
105 views

### Why is a receiving antenna optimal at $\frac{\lambda}{2}$, mathematically?

I can understand the qualitative argument of a recieving antenna becoming resonant: An external $E$-field causes the charges to move in a conductor and bunch up, creating a voltage. If the driving $E$-...
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### Why terms proportional to derivative of EM $A_\mu$ field do not explicitly appear in the Dirac Eq?

In Dirac Eq in presence of EM field we normally include the minimal coupling based on $U(1)$ symmetry argument, as $$\gamma_\mu (\partial_\mu +\frac{ie}{\hbar c} A_\mu) + \frac{mc}{\hbar}.$$ Now I am ...