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: Basic Potential Difference Problem

  1. Aug 28, 2009 #1
    1. The problem statement, all variables and given/known data
    What potential difference is needed to stop an electron having an initial speed of 4.2*10^5 m/s?

    2. Relevant equations
    W = delta K
    W = q*delta V

    3. The attempt at a solution
    So I'm pretty sure that the potential difference should be negative in order to stop the electron, but I keep getting a positive answer (the correct magnitude, but incorrect sign).

    I set delta K = q*delta V.

    I know delta K will be less than zero since K(final) < K(initial) and q should also be negative since we're dealing with an electron. But this gives me a positive delta V.

    Where am I going wrong?

    Thanks in advance.
  2. jcsd
  3. Aug 28, 2009 #2


    User Avatar
    Homework Helper

    so you have 1/2 mv2=VQ

    for an electron Q=-1.60*10-19C
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook