# Homework Help: Find the de Broglie wavelength of an electron

1. Sep 4, 2006

### Reshma

Find the de Broglie wavelength of an electron with KE:
a]10eV
b]1KeV
c]1MeV
d]100MeV

Formulae:
Relativistic
$$\lambda = \frac{h}{\sqrt{{(E/c)}^2 - m_0^2c^4}}$$

Non-relativistic
$$\lambda = \frac{h}{\sqrt{2mE}}$$

I am wondering for which case(s) should I apply the relativistic or the non-relativistic equation given that the BE of electron is 0.511MeV.

2. Sep 4, 2006

### inha

The nonrelativistic approximation is generally good enough until the KE is about 5 or 10% of the rest energy.

3. Sep 4, 2006

### Andrew Mason

If the energy of the electron is much less than this, the electron is non-relativistic. Otherwise use the relativistic formula.

AM

Last edited: Sep 4, 2006
4. Sep 5, 2006

### Reshma

Thanks inha and Andrew for the help!