Wavelength, Frequency

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Air
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Hello, I confused as there are 2 very similar equation but I do not know when to use each of them. They are:

[itex]f = \frac{v}{\lambda}[/itex] and [itex]f = \frac{c}{\lambda}[/itex].

What is the difference between [itex]c[/itex] and [itex]v[/itex] and when can the appropriate one be used? :confused:
 

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ZapperZ
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Er... one is for a particle or wave at any velocity v, while the other is when v=c (i.e. light in vacuum).

Zz.
 
Air
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Also, can [itex]c[/itex] also be used when we are considering other source of waves (e.g. electromagnetic spectrum)?
 
ZapperZ
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When I use the word "light", I do mean the EM wave, not just "visible light".

Zz.
 
GT1
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Why do short wavelengths usually penetrate deeper then long wavelengths ?
(I know it has more energy, but I'm looking for more detailed explanation after reading the FAQ).
 
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Why do short wavelengths usually penetrate deeper then long wavelengths ?
(I know it has more energy, but I'm looking for more detailed explanation after reading the FAQ).
Said that way it's not true, in general: it depends on material, its surface conditions, and on the range of frequencies; in some cases it could be the opposite.
 
GT1
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Said that way it's not true, in general: it depends on material, its surface conditions, and on the range of frequencies; in some cases it could be the opposite.
So if choose randomly 10000 materials only on 50% of the cases the short wavelengths will penetrate deeper ?
 
ZapperZ
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So if choose randomly 10000 materials only on 50% of the cases the short wavelengths will penetrate deeper ?
Look at one of the most common material on hand - ordinary, transparent glass that you can buy at a store. It allows for the transmission of almost all visible light spectrum, but it doesn't allow UV to penetrate. And UV has a shorter wavelength than visible light.

Your question can't be answered because almost all materials have a finite bandwidth of absorption and/or transmission. This means that there isn't usually a "trend". While some wavelengths smaller than something may get transmitted, other that are smaller or longer may not.

Zz.
 

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