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: Homework -- wavelength associated with a neutron moving with energy of 2ev

  1. Oct 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Calculate the de - Broglie wavelength associated with a neutron moving with energy of 2ev .( mass of proton mp= 1.67*10^-27 kg )

    2. Relevant equations
    Wavelength= nh/ 2π
    KE = eVs = 1/ 2mv^2
    Wavelength= v*f

    3. The attempt at a solution
    To calculate the wavelength at first I required velocity that I got from second equation.
    I substituted mass of proton since its equal to that of neutron.
    Then I got the frequency from third equation and put it in equation fourth.
    But I didn't get the required answer.
    De- Broglie wavelength is associated with first equation . so I am confused with it
    I will really appreciate your help.
    Last edited by a moderator: Oct 26, 2015
  2. jcsd
  3. Oct 26, 2015 #2

    Mister T

    User Avatar
    Science Advisor
    Gold Member

    Weird that they give you the mass of the proton. Likely it's a typo. You can use that value as the mass of the neutron as it's essentially the same.

    Look up the definition of the deBroglie wavelength.

    ##\frac{nh}{2\pi}## is the angular momentum of an electron in the Bohr atom, it's not a wavelength.

    ##hf## is the energy of a photon, a massless particle that moves at speed c. It's not the energy of a massive particle such as a neutron that travels at a speed less than c.

    ##\frac{v}{f}## is the wavelength of a wave of frequency ##f## moving at speed ##v##.
    Last edited: Oct 26, 2015
  4. Oct 27, 2015 #3
    [Moderator's note: Fixed a broken quote tag]
    Oo. Thank you. I got it
    de-broglie wavelength is h/ mv and v=
    Putting the values I got the answer as
    2.02*10^-11m . but the answer given is 6.4*10^-13 . I think I messed up somewhere. I want some help.thank you.
    Last edited by a moderator: Oct 27, 2015
  5. Oct 27, 2015 #4


    User Avatar

    Staff: Mentor

    Can you check your question source to confirm the given energy of the neutron? Was the value given in eV or keV?
  6. Oct 27, 2015 #5
    The energy is given in eV
    I checked two sources. But I got the correct answer with 2kev .
    Thank you very much for the hint.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted