# Tag Info

18

The speed of light is always c in vacuum, when measured locally, independent of the wavelength. Though, in a medium, the index of refraction is n=c/v. Speed of different em radiation in a medium Now if the index depends on the wavelength, then different wavelength (color) light has to have different speeds in the medium. In optics, the refractive index ...

5

The speed of a wave is given by: $$c=f\lambda$$ Where $c$ is the speed of the wave, $f$ is the frequency and $\lambda$ is the wavelength. You're right that different colours have different frequencies, but light with a lower frequency has a longer wavelength, in other words if $\lambda$ goes up then $f$ has to come down so they cancel each other out and ...

4

Imagine that you have a great big loudspeaker on top of a mountain, with a switch that makes the loudspeaker cone jump into one of two positions. When you flick the switch down, the cone jumps forwards and sends out a positive pulse, and when you flick it up, the cone jumps back again and sends out a negative pulse. The speed at which your standard pulses ...

3

Well, UV-C surely carries more energy than UV-A and UV-B, but the reason as to why UV-C radiation doesn't reach Earth is because of the presence of $O_2$ and $O_3$ in the stratosphere. UV-C radiation carries enough energy to excite an electron present in the oxygen molecule to shift to a higher energy orbital in the same oxygen molecule. Almost all energy ...

3

A matter of thresholds The reality of spread-spectrum is complicated but let's imagine that the WiFi router and cell phone tower have both allocated 1 Watt to transmit to your phone, and it in turn can transmit 1 Watt back in both cases. If the WiFi router is 10 meters away and the cell phone tower is 1 km away, then it's possible to imagine a four order ...

3

It is very important to understand the difference between electromagnetic waves and static electromagnetic fields. You are asking about why rocks are intact without visible light, and the answer is that the EM force that is needed to hold material like rocks (and give covalent bonding for their molecules) together is represented by static EM fields that are ...

3

Yes. All photons transfer energy, so all photons can cause an object to heat up. Energy is related to frequency by the equation $E=hf$, where $h$ is Planck's constant. This means that a higher frequency photon carries more energy, so a gamma photon carries more energy than a radiowave photon.

3

No, they are related by the formula $$c_0 = f \cdot \lambda$$ with speed of light in vacuum $c_0$, frequency $f$ and wavelength $\lambda$. A change in frequency demands an anti proportional change in wavelength and vice versa, since the speed is constant. It is not possible to change the frequency and leave the wavelength constant. This is quite ...

2

Do all wavelengths of light carries ‘heat’ (thermal radiation) with them? One needs a definition of "carries" . The wavelengths of classical electromagnetic waves that are considered thermal radiation are the infrared wavelengths in the table If yes then can you please tell me, “Which carries more heat, a single photon of gamma wave or a single photon of ...

2

The question could be re-phrased to make it clearer or more precise, but the gist of it is clear enough. The OP is asking whether relative clock rate, which changes with distance from a gravitating mass, is sufficient to explain gravitational lensing. It's not useful to say "No, a light ray follows a geodesic in curved space", because the change of relative ...

1

I just want to comment on one point and this probably will not answer your question completely. LF frequencies correspond to very large wavelengths such that LF waves have wavelengths that match the geometrical extent of vertical refractive distribution of the atmosphere. This provides the travelling LF wave to couple to the surface (does not travel straight ...

1

I misread the frequency in the question and will edit out the portion of my response here dealing with extra low frequency RF penetration of the earth, since I cannot delete the whole thing. Regarding how far from the sun ELF signals can be propagated, the answer is a very big number, but note the following: the readability of a given signal depends not ...

1

We can easily see without a calculation that this mass-energy is negligible compared to the mass-energy of the stars. The galaxy is somewhere on the order of $10^4$ light years in size. That means that a star's light spends $\sim10^4$ years inside the galaxy before it's gone. So the ratio of the mass-energy of the light in our galaxy to the mass-energy of ...

1

The only thing is needed to assume coherency is that the reflection phase $\alpha$ be independent of the instantaneous frequency across the bandwidth of interest. As long as that holds the reflection phase can be ignored. The reflection phase as long as it is constant plays no role in matched filter detection since it shows up as a simple constant ...

1

Short-short answer: "No." Your proposal fails to conserve lepton number, fails to account for the observed energy distribution of the products, and is contradicted by direct observation of "inverse beta decay" events in large, low-background detectors (which would see the incident photon flux if such a thing were responsible, and would block any photon of ...

1

The two forms are not equivalent; the second is wrong. In the book you refer too, "effective" does not mean relative. Effective here is in the sense that we have a model for the permittivity and that the material acts as if the permittivity is the one given by the model. As it can be seen from the previous equation 1.14.1, the author talks about the ...

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