All Questions
Tagged with electromagnetic-radiation wavelength
206
questions
15
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7
answers
2k
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Why does the length of an antenna matter when electromagnetic waves propagate perpendicular to the antenna?
The optimum length for a dipole antenna is a multiple of half the wavelength that it is designed to receive or emit. Why is this? If an electromagnetic wave has E in the x-axis, B in the y-axis, and ...
- 161
11
votes
4
answers
2k
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Can the laser light, in principle, take any wavelength in the EM spectrum?
Can the laser light, in principle, take any wavelength in the EM spectrum? I don't think there is what prevent this in principle, right?
- 959
8
votes
4
answers
2k
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How can photons interact with nuclei?
How can photons such as X-rays or gamma rays interact with the nuclei of atoms given that, as I understand it, the length scale of a nucleus is around a couple of femtometers? So, shouldn’t the size ...
- 133
2
votes
0
answers
30
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Why does oxygen green (S1) emission in aurorae only occur at lower altitudes? [duplicate]
Aurorae have a red color at high altitudes caused by the excitation of atomic oxygen and the subsequent emission at about $630 \,\text{nm}$. This happens at high altitudes because at that height there ...
- 181
7
votes
5
answers
14k
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Light waves can't have a wavelength
The wave nature of light comes from Maxwell's equations. More precisely, the two wave equations that come from them:
$$\Delta\vec{E}=\mu\varepsilon \frac{\partial^2\vec{E}}{\partial t^2}\\
\Delta\vec{...
- 267
1
vote
2
answers
52
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Minimum frequency for a dipole antenna to work
Does a dipole antenna need a minimum frequency of AC to make the electric field detach and propagate?
- 156
1
vote
1
answer
41
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How is wavelength defined when it's changing continuously?
Take an observer, who is receiving an electromagnetic wave signal, which is constantly changing. It can be for example from a source of light falling into a black hole, so the observed wavelength is ...
- 13
0
votes
1
answer
44
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Emission spectrum of a fluorescent lamp
I had to analyze the emission spectrum of a compact fluorescent lamp and find what elements are present in the lamp, based on the spectrum of spikes in wavelengths. Knowing that in our lamp there was ...
-1
votes
2
answers
80
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What's the difference between the different kinds of EM waves?
I am an A-level student.
We have traditionally been taught that different types of EM waves exist only between certain ranges of wavelengths and frequencies.
However, I learned that electromagnetic ...
1
vote
1
answer
61
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In Rayleigh-Jeans radiation law, why are the values of $n$ taken to be non-positive only?
In $k$-space the allowed values for standing waves in a cube of side length $L$
are given by
$$\vec{k} = \left(\frac{\pi}{L}\right) (n_1, n_2, n_3)$$
where the $n_i$ are nonnegative integers. Why are ...
- 11
1
vote
1
answer
26
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Spectroscopy on colored flames
When observing colored fire through a spectrometer after adding substances like copper chloride or magnesium sulfate to change its color, what specific spectra are typically observed? How does the ...
- 43
0
votes
1
answer
39
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What determines the wavelength in absorption?
When looking at absorption or reflectance spectra, say in the range of 400nm to 2500nm, you can see peaks (or dips) at certain wavelengths, that are characteristic for the material absorbing and ...
- 111
15
votes
6
answers
7k
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Why color depends on frequency and not on wavelength? [duplicate]
To explain my question lets consider this example:
The wavelength of light in a medium is $\lambda=\lambda_{0}/\mu$, where $\lambda_{0}$ is the wavelength in vacuum. A beam of red light ($\lambda_{0}=...
- 2,517
2
votes
2
answers
96
views
Does gravitational lensing bend light of all wavelengths by the same amount?
Basically I am asking if gravitional lensing is bending or refracting light.
- 319
0
votes
1
answer
88
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What is the wavelength range of X-rays?
I was reading and came across the following paragraph
The X-rays thus produced by many electrons make up the continuous spectrum of Figure 2-10 and are very many discrete photons whose wavelengths ...
- 959
8
votes
4
answers
3k
views
Do colours which are not visible to human eyes exist?
Are there any colours that our human eye cannot comprehend but other animals can see? The ability to see colours is the property of our eyes. For example an average dog would see less colours than us. ...
- 412
2
votes
1
answer
682
views
Why can't we use polychromatic light for making laser?
As far as I have read in my textbooks, we can only use monochromatic light for making a laser. Why can't we use polychromatic one? What if we try to make a laser out of a polychromatic light?
1
vote
3
answers
72
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Wavelengths of light outside our solar system
The question might have been asked before. Our Sun's rays decompose into 7 elementary colors by using a prism or spectrometry. Can the the colors (their number and wave length in the spectrum ) be ...
- 1,032
0
votes
1
answer
142
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What is the smallest possible wavelength? [duplicate]
I was thinking about this the other day after a quantum mechanics lecture (unrelated to the lecture I was taking) and pondered "Is there a minimum wavelength for a photon?", through ...
- 13
0
votes
2
answers
70
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Why do parabolic antennas need to be the same width as their wavelength?
I am reading the wikipedia page for parabolic antennas, and have a question about the below quote:
In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the ...
- 137
1
vote
1
answer
187
views
Can something become hot enough that it stops glowing?
So I understand that matter emits EM waves when hot. And that the higher the temperature, the shorter the wavelength, so cooler flames start off orange and the hotter flames reach light blue and white....
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1
vote
1
answer
63
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If the speed of light is a constant value and the wavelength is constant (antenna), how can one antenna transit/receive different frequencies?
The speed of light is about 300,000,000 m/s, and the wavelength is determined by the design of the antenna, how can one antenna transmit different frequencies other than just the one defined by
f = c /...
- 13
6
votes
3
answers
743
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When designing antennas which speed of light should be used?
When calculating "antenna element length" should we use the speed of light in the "medium between transmitter and receiver (antenna)" or the speed of light in the "element ...
- 613
2
votes
1
answer
220
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How do we know the wavelength and frequency of electromagnetic wave? [closed]
From my understanding, the frequency and wavelength of a mechanical wave can be observed by the motion of the particles (i.e., as the particles oscillate from their state of equilibrium, the wave ...
2
votes
1
answer
122
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Antennas and Wavelength
I'm clearly missing something here, but I'm trying to grasp basics of how antennas work.
Relating it to standing waves on a string of length L, the lowest frequency possible is a wavelength of 2L, due ...
- 111
-1
votes
1
answer
67
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The connection between kink and wavelength
As we know, in EM wave, with the oscilation charge (for simplicity, charge was moving at constant speed, then accelerated and then continued moving with constant speed again), kinks are produced. The ...
0
votes
0
answers
34
views
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 ...
- 11
3
votes
3
answers
654
views
How can infrared light interact with nerve cells given the wavelength is so much longer than the cell's size?
I obviously do not understand how a wavelength greater in length than a cell can be detected by a cell.
As I understand it, infrared ranges from 300GHz to hundreds of THz.
As an example, if an ...
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-1
votes
2
answers
152
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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}.$$
It's defined as energy emitted per unit volume per wavelength. I'm not sure if this includes per solid angle, but I ...
- 200
0
votes
1
answer
110
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Max Planck - what's the $B$?
Planck says
$$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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