1. Not finding help here? Sign up for a free 30min 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!

Finding Electric Field intensity

  1. Jul 17, 2010 #1
    1. The problem statement, all variables and given/known data
    A proton travelling along the x-axis is slowed by a uniform electric field E. At x = 20 cm, the proton has a speed of 3.5 x 106 ms-1 and at x = 80 cm, its speed is zero. Find the magnitude and direction of electric field intensity.

    Can someone please!!!! check my procedure and if your really nice/helpful my answer-----thanks.


    2. Relevant equations
    W=Fx
    W=Eqx
    W=ΔK_E
    ΔK_E=1/2 mv^2-1/2 mu^2



    3. The attempt at a solution
    1st i found the change in energy (work) to slow the proton to a stop. then thats equal to Eqx. I found E to be 1.06*10^5 N/C (positive direction) please check my answer if you have time - its worth marks.
     
  2. jcsd
  3. Jul 17, 2010 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    The magnitude of the electric field is correct. In what direction should the force on the proton be and why?
     
  4. Jul 17, 2010 #3
    thanks kuruman - I thought positive (is that whats meant by direction??) because they need to be "like" to repel??
     
  5. Jul 17, 2010 #4

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    I am talking about the force on the proton. If it moves left to right (x is increasing), in what direction should the force be to stop it?
     
  6. Jul 17, 2010 #5
    towards the origin - - but left or right would be dependent on the way the cc were defined???? +x could be towards the left or right couldn't it???
     
  7. Jul 17, 2010 #6

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Yes it could, so let me rephrase my question. Relative to the direction of the proton's velocity, in what direction should the force on it point? Same or opposite direction? The answer to this question has nothing to do with which way is positive and which way is negative.
     
  8. Jul 17, 2010 #7
    opposite to slow it down??
     
  9. Jul 17, 2010 #8

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    Yes. Now how is the direction of the force on a positively charged particle related to the direction of the electric field? Same or opposite?
     
  10. Jul 17, 2010 #9
    same- the direction of an electric field is the way a positively charged test particle would go
     
  11. Jul 17, 2010 #10

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    So put it together. Is the direction of the electric field the same as or opposite to the direction of the proton's velocity?
     
  12. Jul 17, 2010 #11
    so the full answer is 1.06*10^5 N/C in the opposite direction of the protons velocity.
     
  13. Jul 17, 2010 #12

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    That is correct.
     
  14. Jul 17, 2010 #13
    thanks kuruman!!!!!!!!!!!!!!!!!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding Electric Field intensity
Loading...