# Homework Help: De broglie

1. Oct 31, 2005

### asdf1

how do you find the kinetic energy of an electron whose de Broglie wavelength is the same as that of a 100keV x-ray?

2. Oct 31, 2005

### El Hombre Invisible

Since the de Broglie wavelength is given by the momentum of the particle, I guess you would first determine the momentum p of the photon: p = E/c (I think), then find the kinetic energy of the electron via 0.5p^2/m, where m is the electron mass.

3. Nov 1, 2005

### asdf1

it's not a photon, but can you still use that formula?

4. Nov 1, 2005

### El Hombre Invisible

Yes, you can use the de Broglie formula h/p to find the wavelength of an electron or a photon. The difference between the two comes in determining p. For an electron, p = mv. For a photon, p = E/c.

So if your photon has energy E = 100 keV, convert this to Joules and use p = E/c to find the momentum of the photon.

If the de Broglie wave of the electron has the same wavelength, it must have the same momentum p.

5. Nov 1, 2005

ok, thanks!