All Questions
34
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Effective aperture as a function of Azimuth and Elevation Angle
Wikipedia says
The effective aperture of an antenna is given by $$A_{\mathrm{e}}(\theta, \phi)=\eta A \cos \theta \cos \phi ,$$
where, $(\theta, \phi)$ are the azimuth and elevation angles relative to ...
- 101
2
votes
0
answers
34
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Multipole radiation of a wave
I read that a sound wave (a scalar wave) produces monopole radiation, an eletromagnetic wave (a vector wave) produces dipole radiation, and a gravitational wave (a second order tensor wave) produces ...
- 687
4
votes
2
answers
788
views
How do non-periodically varying currents produce electromagnetic waves?
Electromagnetic radiation is created by the varying/accelerating of a system of charges and currents. Suppose that the time dependence of the charges and currents are $\rho(x,t)$ and $J(x,t)$. Then ...
- 324
3
votes
1
answer
165
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Can point masses following geodesics and orbiting one another emit gravitational radiation?
I am a bit confused about this situation: according to general relativity, when two masses orbit one another, they emit graviational waves, which carry away certain energy. For example, check out ...
1
vote
1
answer
40
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Interference of standing waves inside black body?
Does electromagnetic wave inside a cavity (modeling black body ) interfere with each other?
And why in the derivation of Rayleigh law of black body radiation we add energy of different modes (are we ...
1
vote
1
answer
58
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Interference of em waves
If EM waves interfere, how is it that wave that is in my line of sight does not interfere with wave that is in someone else's line of sight which intersects my line of sight, and consequently make ...
- 35
1
vote
2
answers
259
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Near field and Far field
in EM radiation, it is generally considered that if $D \ll \lambda$, $D \ll r$ and $r \gg \lambda$, it is radiation zone ($D$ is the antenna's length). I can't seem to see how that fits the Fraunhofer ...
- 1,038
1
vote
1
answer
578
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How can the amplitude of a wave determine if it is plane, spherical or cylindrical?
it's known that typical expressions for plane, spherical and cylindrical waves are (for instance in terms of electric field uniformly propagating along r axis, in frequency domain):
Plane Wave: $E(r) ...
- 1,319
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1
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156
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Where does the proton's kinetic energy go when a proton and nuclei are fused together to create a heavy nucleus? I cannot solve this problem
The problem then states: estimate the minimum wavelength of the gamma ray photon.
The answer to this question is: 0.25 x 10^-11 - (binding energy of oxygen - the binding energy of F which is 0.04 x 10^...
- 220
3
votes
1
answer
61
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Shield gamma/X-ray/ultraviolet radiation without blocking radio waves
I was theoretically considering building an airtight enclosure that shielded the insides from gamma/X-ray/ultraviolet radiation but did not block radio waves (so that communication would not be ...
- 131
0
votes
1
answer
106
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What do the ideal blackbody and a generic colored body have in common?
as you know, the ideal black-body has a lot of interesting properties. The most important of these is surely the Planck Law about its radiation:
Clearly the concept of black body does not exist ...
- 1,319
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49
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How to explain light beams in terms of wave theory?
How can we explain the formation of light beams in terms of wave theory?
According to wave theory, shouldn't the source point of beams emit radiation omnidirectionally, rather than a concentrated ...
- 533
1
vote
1
answer
120
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Poynting vector interpretation
I am trying to calculate the dynamics of the power density of light in vacuum. The absorption per unit volume defined in terms of the Poynting vector is given by:
\begin{equation}
\text{Absorption} = -...
- 11
1
vote
2
answers
1k
views
How does particles move in waves? radiation?
I'm reading about particles for a project and had a question. I read that particles don't move forward in a wave, the simply oscillate up and down, and that gives it the wave look. But if they don't ...
- 603
4
votes
4
answers
4k
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Wavelength and penetration by EM radiation
I'd like you to clarify the relationship which relates penetration power by EM radiation with its wavelength (or inverse of frequency).
Suppose we conduct an experiment, irradiating a body with ...
- 194