Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Momentum of particle

  1. Dec 23, 2011 #1
    Say I have the rest energy(mc^2) and the total energy of a particle (E), would getting the momentum energy of the particle be as simple as doing (E^2-(mc^2)^2)^(1/2) = pc?

    And when accelerating a electron through a potential difference how would I work out its momentum, given I have its rest energy and the value for potential difference?

  2. jcsd
  3. Dec 23, 2011 #2
    That looks like the correct equation to use.

    When an electron is accelerated through a potential difference, what happens to its total energy?
  4. Dec 23, 2011 #3
    c=1 you have
    E2= p2+m2

    so you want to know the momentum you do what you said

    p=√ [E2-m2]

    by the time you say "total energy E" it means that the kinetical energy is within your already known parameter, so is there a potential, is there not- you know E, you know mass, so you know its mommentum.
  5. Dec 23, 2011 #4
    I am assuming that for a p.d. of for example 1 MV, this will create an energy difference of 1 MeV for an electron and with the rest energy of around 0.5 MeV for an electron, it would simply equal 1.5 MeV/c for the momentum, but I think this is wrong, but I don't understand why.
  6. Dec 23, 2011 #5


    User Avatar
    Science Advisor
    Gold Member

    Assuming all the energy was kinetic, your formula works. If there is also potential energy involved, then you have to take that into account as well.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook