# The fomula h/lambda is this for the photon only?

1. Feb 25, 2006

### UrbanXrisis

the fomula $$\frac{h}{\lambda}$$

is this for the photon only? or can it be applied to relativistic electrons too?

2. Feb 25, 2006

### anjor

it applies to particles with zero rest mass. Hence it wont apply to relativistic electrons.

3. Feb 26, 2006

### UrbanXrisis

so for relativistic electrons, if I wanted it's speed, i'd use .5mv^2?

4. Feb 26, 2006

### dicerandom

1/2 m v^2 only works for non-relatavistic speeds, the energy for a relatavistic particle is different. See here for more details.

5. Feb 26, 2006

### gulsen

Same question was asked by de Brolie. And actually, it turned out that it will.

6. Feb 26, 2006

### topsquark

Yes, but UrbanXrises' original formula was either a typo or assumed that c=1. With c=1 this formula is, in fact, only good for massless particles. DeBroglie's relationship involves the speed, which is less than c.

-Dan

7. Feb 26, 2006

### gulsen

No, it comes from:
$$E = pc = \frac{hc}{\lambda}$$
where c's cancel, and de Broglie's equation relates momentum and wavelength.

8. Feb 26, 2006

### topsquark

I was thinking of the energy equation. Sorry! (Ahem!)

Even though I got my c's wrong, the argument still holds...E=pc only hold for massless particles, which was what I was trying to say.

-Dan

Last edited: Feb 26, 2006
9. Feb 26, 2006

### UrbanXrisis

so $$p=\frac{h}{\lambda}$$ is for massless particles

but what about $$E=fh$$?

is this equation for massless particles too?

10. Feb 26, 2006

### topsquark

No. This equation is good for anything. Basically this equation simply expresses the quantizability of energy.

-Dan

11. Feb 27, 2006

### gulsen

No, it applies to all particles! That's the backbone for Schrödinger equation!