# De broglie wavelength

1. Mar 10, 2007

### xiankai

since it is defined (from what i can tell) as h/p,

is it interchangeable with the classical wavelength in equations involving waves in general? or is it a special separate case for matter?

that is,

for photons we have the following equation:
E = hf
E = hc/λ

can the same equation be used to find the wavelength/energy of electrons?

2. Mar 10, 2007

### StatMechGuy

The de Broglie wavelength is now kinda viewed as the characteristic "size" of a quantum particle. It's not really a super-relevant physical quantity anymore, nor can you just put it into classical wave equations to get anything physical.

3. Mar 10, 2007

### Meir Achuz

For a photon E=pc, so the dB wavelength for a given energy is simple.
For an electron p=\sqrt[{E^2/c^2-m^2}, so the dB wave length in terms of energy is more complicated,.

4. Mar 10, 2007

### xiankai

we must include the rest mass of the electron?

5. Mar 11, 2007

### Staff: Mentor

Yes. And to get the frequency of the wave via E = hf, you must use the total energy (kinetic energy plus rest energy).

6. Apr 16, 2007

According to de broglie relation lambda=h/mv ...which implies that velocity is inversely proportional to wavelength. But According to the reletion

V=n lambda ... velocity is directly proportional to wavelength...... How That diffenence is Causesd ? Am i going wrong Somowhere ?

7. Apr 16, 2007

### Hootenanny

Staff Emeritus
Note that the wave relationship only holds for massless particles.

8. Apr 17, 2007

### Meir Achuz

The V in V=\nu\lambda is the phase velocity of the traveling wave packet.
This V also = E/p=h\nu/p, which is consistent.
The phase velocity is >c, but the group velocity v_G=p/E is less than c.