/sci/ - Science & Math

[Anonymous No.6535290]

Hi just a quick question about physics..

I had this quite self-explanatory question on physics exam: "What decides the frequency?" answer was: "Source of the frequency" , I was like.. no shit sherlock.. But then I started to wonder (and googling) what actually controls the frequency..

For example we have a 10f (frequency) lazor how can we control it to be 9f (frequency), can we control it anyway? What in this lazor decides that it is its frequency?

I know what frequency is, and its pretty impossible to control frequency without the right equipment for example red lazer cant be green lazer etc.. But like what the hell of a kind question (in that exam) was that in the first place; what controls the frequency??

[Anonymous No.6535299]

The frequency of light is dependent on the energy of the photons. In a LASER photons are created by electrons jumping between energy levels. LASERs are special because they get a bunch of atoms that are good at making their electrons jump between the same energy level over and over which produces a photon of a specific energy (which also means same frequency).

Even outside of light, frequency is generally dependent on energy in some way.

[Anon No.6535305]

>>6535290
The frequency is determined by the amount of energy expended at the moment the photon was brought into being. More energy = higher frequency.

Typically, light is the result of electrons becoming excited, jumping between the energy states around atomic nuclei. When an electron goes from a higher energy state to a lower one, it lets off a little bit of light. If it loses a little bit of energy, it gives off low-frequency light. Losing more energy makes it give off higher-frequency light.

For information about lazors, visit this page:
http://www.thefreedictionary.com/lazor

[Anonymous No.6535311]

>>6535299
>>6535305
Uu interesting :)

Thank you guys.

So the more correct answer to "What determines the frequency" (controls/decides whatever)

Would be: "The energy of the Frequentic Source"?

[Anonymous No.6535339]

>>6535311
..or the energy of the frequence?

Can we control the frequence by giving more energy to the source or to the frequence itself?

[Anonymous No.6535344]

>>6535290
>For example we have a 10f (frequency) lazor how can we control it to be 9f (frequency), can we control it anyway? What in this lazor decides that it is its frequency?

Look into frequency combs. Using a single laser at a given frequency f as a reference, frequency combs create a series of "teeth" with spacings of d: i.e. you essentially have a bunch of lasers with frequencies of f+n*d for integer n. In total, the envelope of frequencies spans about an octave. By choosing the right value for d [basically determined by the cavity you use], you could have an n such that f+n*d was exactly 9*f/10, which is what you wanted.

[Anonymous No.6535472]

>>6535344
..what? Can I get this drawn/imaged please :) It would explain a lot better and I bet you might also learn something new doing it! <3 Please..

[Anonymous No.6536732]

>>6535311
For light: Energy=h*frequency where h is a specific constant (Planck's constant), so you can say that the frequency of the wave is proportional to the energy source.

Light is a special wave though because it will always have the same velocity and that is what allows the simple E=hf equation above to work. If you were to make a wave on a piece of string or using a slinky, the frequency would depend on how fast you move your arm up and down, so that more directly relates to your exam question (the source of the frequency is your arm moving up and down). So if you move your arm up and down once every 2 second you will create a wave with a frequency of 0.5Hz. The energy of a string wave is related to the amplitude of the wave which would be how far up and down you move your arm- (I am kind of lying here, it is actually related to the mass*amplitude^2*frequency^2 then* wavelength to get an Energy of certain wavelengths, you can think of it as the mass of the string* velocity of the string going up and down squared [not the velocity of the wave]). The moral of the story here is that energy and frequency aren't simply related for mechanical waves.

So summary: Light is special and the energy of the wave determines the frequency. The frequency of mechanical waves like on a string is determined by how often the thing that is moving back and forth to create the wave moves back and forth.