# Homework Help: Quantum physics and wave lengths

1. Jan 22, 2009

1. The problem statement, all variables and given/known data
What is the de Broglie wavelength of an electron that has been accelerated through a potential difference of 1 MV ( you must use the relativistic mass and energy expressions at this high energy.)

ans. 8.7 x 10^-13

2. Relevant equations

M= Mo/ square root (1 - v^2/c^2)

3. The attempt at a solution

I have no idea where to go with this question i am completely stumped, can someone please steer me in some direction to understanding such and getting the right answer, thank you and i really appreciate it.

Last edited: Jan 22, 2009
2. Jan 23, 2009

### buffordboy23

The question offers plenty of clues of where to start.

The desired answer is the de Broglie wavelength. Therefore, you could start at the end and work backwards. Do you know any equations for the de Broglie wavelength that might help you solve the problem? I know one that sticks out immediately; this equation relates the wavelength to only one other variable. Once you determine what this variable is, can you link it to the given data of the problem? If so, then problem solved.

3. Jan 23, 2009

well i assume now you use wavelength= h/mv and to find v i'd use Ee=Ek, just i need to find relativistic mass and energy first for the speed ill get is faster then that of light

4. Jan 23, 2009

### buffordboy23

Here is an important difference for the momentum: p = mv (non-relativistic), p = $$\gamma$$mv (relativistic).

De Broglie's original formula is

$$\lambda = \frac{h}{p}$$