De Broglie Wavelength of Electron

1. Mar 22, 2007

amcca064

1. The problem statement, all variables and given/known data
Ok, question is: " Calculate the de Broglie wavelength for an electron that has kinetic energy a)50.0 eV b) 50.0 keV and c) 3.00 eV d) What If? A photon has energy 3.00 eV. Find its wavelength.

2. Relevant equations

E=hf

1/2 m(v^2)

*lambda* = planck's constant / momentum

3. The attempt at a solution

Was just going to use E = hf then find wavelength from f, but realized that v is unknown unless I can use classical equation K=1/2m(v^2) but I was not sure I can do this??? If I can, problem is easy, if I can't... will need some help... Thanks!

2. Mar 22, 2007

Mindscrape

You have the energy, what do you want to find v for? Use the planck's constant with eV in it, and your units should work out.

3. Mar 23, 2007

QuantumCrash

Are you familiar with the De Broglie relationship, or are you studying in advance? ;-)

You need to use the final 2 equations you stated.

From E=1/2 * m * v^2

2E = m v^2
2Em = (m v)^2
2Em = p^2 p=momentum
p = (2Em) ^ 0.5
h/lambda = (2Em) ^0.5

Should be easy to find wavelength with the above equation.

4. Mar 23, 2007

amcca064

mindscrape - don't need v, need v to find p, or at leaast i thought i needed it until I see that I can do what QuantumCrash suggests...

Was not sure if I could use de Broglie wavelength equation WITH Kinetic energy of a particle equation. i.e. Wasn't sure if i could consider electron particle AND wave in the same situationi. I thought maybe had to consider electron only as wave or only as particle depending on situation. But now I see can do both, Thanks for the help!!

5. Mar 23, 2007

amcca064

hahaha just realized that this is what de Broglie wavelength is all about anyways! wave-particle duality. wow, funny