De Broglie Wavelength of Electron

[amcca064]

Homework Statement

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.

Homework Equations

E=hf

1/2 m(v^2)

*lambda* = Planck's constant / momentum

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!

 

[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.

 

[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.

 

[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!

 

[amcca064]

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