# Need Help Remembering An Equation

1. Apr 16, 2009

### Hertz

Does anyone happen to know the equation to convert frequency into energy?
I think it's something like: E = hf, but I'm not sure.

Any help is appreciated :)

2. Apr 16, 2009

### whybother

Yup. I assume you mean for EM waves?

3. Apr 16, 2009

### Hertz

Yup, is that the right equation?

4. Apr 16, 2009

### whybother

Yes.

5. Apr 16, 2009

### Hertz

So this means that mc^2 = hf right?
So does this mean that everything with mass is actually an EM wave? Sorry I don't know a whole lot, I'm still in 11th grade :\

6. Apr 16, 2009

### whybother

No, that's not what it means, that's why I asked if you meant for EM waves.
While yes, all matter does have an associated wavelength, but no, you can't compare the rest mass energy to the energy for an EM wave.

You should read about http://en.wikipedia.org/wiki/Wave-particle_duality" [Broken] if you are curious.

For photons, $$E=h f$$ where the momentum of a photon is given by,
$$p = {E \over c}$$

Generalized to massive particles, we get
$$\lambda = {h \over p}$$

Where $$\lambda$$ is the associated wavelength.

In general, energy is not just the rest mass energy and also includes a momentum term, so for our massive particles we have: $$E^2 = m^2 c^4 + p^2 c^2$$

Last edited by a moderator: May 4, 2017