1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculate the wavelength of electrons traveling at 1.15x10^5

  1. Apr 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Calculate the wavelength of electrons traveling at 1.15x10^5 m/s

    2. Relevant equations
    λ = h/m*v

    Given values:
    h=6.626x10^-34 J*s
    v=1.15x10^5 m/s

    3. The attempt at a solution
    I converted J*s to SI units (kg⋅m2⋅s−2) and then substituted out all known values, to get:
    λ = (6.626x10^-34 kg⋅m2⋅s−2)/(9.11x10^-31kg)(1.15x10^5 m/s)

    After canceling out like units and doing the math, I get:
    λ = 6.00x10^-9m

    The text gives the solution as 6.33nm. I can't figure out how they got there (and why they converted to nm?).

    Is this an error in the text or (more likely) in my logic/calcuations?

    Any/all input is appreciated. Thanks!
  2. jcsd
  3. Apr 26, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your expression is correct, just redo the arithmetic. For wavelengths that small, nm is a typical unit.
  4. Apr 26, 2015 #3
    Ah, good to know about nm... And I'll do the math again (hopefully better!). Thanks :)
  5. May 16, 2015 #4

    James Pelezo

    User Avatar
    Gold Member

    If interested, and using the wavelength determined in the above problem, calculate the amount of energy in 1 gram of electrons moving at the same speed. (See if you can get ∆E = 1.9 x 104Kj/mole e-'s = 3.45 x 107Kj/g e-'s. Compare: A candle flame generating q ~ 40.7 Kj/g from burning paraffin wax to the energy content of a gram of electrons traveling at 1.15 x 105m/s. => You might find it very surprising. You are definitely on the right track. Good job!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted