# Relation between Energy and frequency

1. May 20, 2015

### gianeshwar

Hi Friends!
Please tell me if the question below is valid?

"If the frequency of the source is changed from f to 2f ,keeping amplitude same,then total energy is changed by what amount?"
What I conclude is"We can think it in two ways:
1 In classical sense,where I could not find any such relation.
2 In microscopic(quantum) sense E equals hf where h is Plank's constant .So it can give answer as E if the Energy at f is E.

2. May 20, 2015

### Staff: Mentor

Your question is very unclear. Are you talking about a laser? A power grid? An audio amplifier? Or what?

3. May 20, 2015

### gianeshwar

Consider it in classical sense e.g water wave or rope being vibrated by hand when other end is attached to a wall etc.
I am not an expert but am very keen so please bear me.
I meanwhile stumbled upon a formula
E =pie square.n square.A square.v.
I still do not know its validity.

4. May 20, 2015

### ZapperZ

Staff Emeritus
You seem to have a bit of a problem in presenting a very clear and complete question. It also appears that you are looking at some source and then asking things here.

I suggest you make a reference to the source, i.e. is this out of a book or from some website that you read? Then provide a link.

Secondly, "symbols" mean nothing without context. If I tell you that E in that equation is actually H, and that A square v equal to wk, will that makes ANY sense to you? No? Then look at what you've done!

Without proper definition and context, those symbols that you've typed are meaningless, and you've just wasted time and effort presenting something that not many people can understand.

Try to sit back, and look at what you've typed, and see if you are assuming that we actually know what's in your head.

Zz.

5. May 20, 2015

### gianeshwar

Thank You anorlunda and ZapperZ for responding! I will come back with my clear idea.

6. May 22, 2015

### theodoros.mihos

1D waves we can represent by amplitude as:
$$y(x,t) = A\sin(\omega{t}-kx)$$
where energy depends from A2. On 2D or 3D waves we cannot difine the wave by amplitude, because this is not the same. Let we have circular waves on water surface by a source of power P. The wave function must be:$$y(r,t) = \frac{A}{r}\sin(\omega{t}-kr)$$and we must calculate A by setting the energy gives the source in one period equal to energy have all vibrational particles in the first wavelength.
This is not easy but A can be calculated and the above function can be formed well.

Now if you want the energy for a classical wave, you must determine what energy talking for. This energy depends by the time period you add not by the frequency. For quantum electrodynamics this energy part cannot be anything but makes quanta of hν energy amount. (h is the Plank's constant).