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Magnetic and electrical forces

  1. Apr 3, 2008 #1
    [SOLVED] Magnetic and electrical forces

    1. The problem statement, all variables and given/known data

    1) A proton traveling due north enters a region that contains both a magnetic field and an electric field. The electric field points due east. It is observed that the proton continues to travel in a straight line due north. In which direction must the magnetic field lines point?

    A) North
    B) Down
    C) Up
    D) South
    E) West
    F) East

    2) A proton traveling due west in a region that contains only a magnetic field experiences a force vertically upwards away from the surface of the earth. What is the direction of the magnetic field?

    A) West
    B) East
    C) North
    D) South
    E) Up

    2. Relevant equations

    3. The attempt at a solution

    For #1 i know it isnt up or north I have tried those but this is how i came about those answer: the proton is moving north and the electric field points due east so that would force the proton to to move into the direction of the electric field which is east.... the magnetic field causes the proton to keep moving north but im not really sure how this works...i know it isnt up or north but i dont know how to eliminate the others

    #2- I know i have to use the right hand rule and i came out with south but i dont fully understand how it works so any hints?
  2. jcsd
  3. Apr 3, 2008 #2


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    Homework Helper

    I think you use the left hand rule for both.

    Use the left hand rule to predict the motion of a particle in a magnetic field at right angles to a current

    Right hand rule is for the direction of an induced current.

    Left hand Rule. Place the thumb,first finger (index finger) and second finger(middle finger).

    the first finger points in the direction of the magnetic field. (f for field)
    The second finger points in the direction of the current. (c for current)
    Thumb points shows the motion of the particle.
  4. Apr 4, 2008 #3
    Ok so just to check my answer, I used left hand for #2, laid my hand flat along negative x-axis (west) and then curled my hand together (vertical upward force) and my thumb points in the south direction which would be the direction right?
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