# Relativistic Calculations for De-Broglie Wavelength

1. Nov 12, 2015

### IWantToLearn

1. The problem statement, all variables and given/known data
At what energy will a non-relativistic calculation of the De Broglie wavelength of an electron be in error by 5%? What is this energy for a proton? Comment on your results.

2. Relevant equations
I have two (seemed to be) logical answers for this question, but with different values

how to resolve this, there must be at least one wrong answer

i need a resolution

3. The attempt at a solution
Solution 1

Solution 2

2. Nov 12, 2015

### Staff: Mentor

The second approach has the right relativistic de-Broglie wavelength. It depends on the momentum, not on "the energy above the rest energy plugged into the nonrelativistic expression".

3. Nov 12, 2015

### IWantToLearn

As far as i understand, there is nothing in the first approach states that the De-Broglie wavelength depend in anything but the momentum
in the first approach i replaced the momentum by the kinetic energy, and this is a valid replacement