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!

Particle in an Electric and Magnetic Field

  1. Apr 8, 2013 #1
    1. The problem statement, all variables and given/known data
    An electron has an initial velocity with an x component of zero, a y component of 12.4 km/s, a z component 13.5 km/s, and a constant acceleration of 2.68 x 1012 m/s2 in the positive x direction in a region in which uniform electric and magnetic fields are present. If the magnetic field has a magnitude of 463 µT and is in the positive x direction, find the (a)x, (b)y, and (c)z components of the electric field.

    2. Relevant equations
    Lorentz Force:
    $$\vec{F}_B=q[\vec{E}+(\vec{v} \times \vec{B})] $$
    $$\vec{F}=m\vec{a} $$

    3. The attempt at a solution
    I have managed to get all of them but (a), which seems like it should be the easiest.

    I've found that the magnetic force along the x-axis is 2.4412*10^(-18) N. The cross product of the velocity and the magnetic field along the x-axis is zero. So we have
    $$\vec{F}_B=q\vec{E}_x $$
    so the answer should be roughly 15.238 V/M in the x-direction. What am I doing wrong?
     
  2. jcsd
  3. Apr 8, 2013 #2
    Consider E should be in the -x direction.
     
  4. Apr 8, 2013 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Write F = ma for x, y and z.
    Solve for Ex, Ey and Ez.

    (Can only be done if ay = az = 0 assumed thruout which I guess it is).

    BTW I got the same number for Ex that you did.

    EDIT: whoops, better take barryj's hint!
     
    Last edited: Apr 8, 2013
  5. Apr 8, 2013 #4
    If the electron is accelerating in the +x direction, then the E field is from + to - and has to point in the -x direction.
     
  6. Apr 8, 2013 #5

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Motion seconded and carried.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted