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De Broglie Formula Application

  • Thread starter Pyroadept
  • Start date
  • #1
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Homework Statement


Estimate the wavelength of a 30 keV electron.


Homework Equations


p = h/λ
E = hf

The Attempt at a Solution


The electron has 30 keV of mass-energy.
As it is acting as a particle-wave, E = hf, so f = E/h = 30,000x1.6x10^-19/6.3X10^-34 = 7.619x10^18 Hz

Now, v = fλ, so λ = v/f, but this is where I run into a problem, as I'm not told what speed the electron is travelling at - do I assume speed of light, or is there some other way?
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
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Estimate the wavelength of a 30 keV electron.

Now, v = fλ, so λ = v/f, but this is where I run into a problem, as I'm not told what speed the electron is travelling at - do I assume speed of light, or is there some other way?
Hi Pyroadept! :smile:

If you can convert the eV into J, and if you know the mass of an electron, then you can calculate the speed from the energy. :wink:
 

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