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Homework Help: Magnetic Fields

  1. Mar 19, 2007 #1
    A proton travels with a speed of 3.00 x 10^6 m/s at an angle of 44.0° with the direction of a magnetic field of 0.730 T in the +y direction.

    (a) What are the magnitude of the magnetic force on the proton?
    (b) What is its acceleration?

    Ok for magnitude of force,

    I used F = qvB sinø
    = (1.6E-19)(3E6)(.73)sin44
    = 2.437 E-13

    But I was unable to find an equation for aceleration in a magnetic field in my notes, can anyone help me out?

  2. jcsd
  3. Mar 19, 2007 #2
    What does the path of the motion look like?
  4. Mar 19, 2007 #3
    lol i have no idea,
    but could this be solved just by using Fnet = ma
    where Fnet incorporates the magentic force and gravitational force?
  5. Mar 19, 2007 #4
    I doubt you need to include gravitational effects here.
    The path of the motion is a hint as to how to find the solution. Any guesses?
  6. Mar 19, 2007 #5
    well i kno initially its moving at the angle of 44˚, but the magnetic field should affect it to move in the positive y direction i think
  7. Mar 19, 2007 #6
    Oh, you need to revisit the right hand rule to determine the direction of the force. This is an important effect for these types of problems.
  8. Mar 19, 2007 #7
    but wouldnt using the RHR in this case introduce the 3rd dimension, because it would be coming out ?
  9. Mar 19, 2007 #8
  10. Mar 19, 2007 #9
    yes, from the cross product.
  11. Mar 19, 2007 #10
    so if we know it is coming out, how does it help solve for acceleration?
  12. Mar 19, 2007 #11
    So at that point the force is out, does it remain in that direction?
  13. Mar 19, 2007 #12
    i assume so
  14. Mar 19, 2007 #13
    If the object has a net force acting on it, it will accelerate in that direction. So the velocity changes; remember that the direction of the force is dependent on the direction of the velocity vector, which changes.
  15. Mar 19, 2007 #14
    so is there a way/formula to solve for acceleration by knowing this?
  16. Mar 19, 2007 #15
    Sorry, if you are looking for me to give you a formula to plug numbers into, I cant help you.
    If you understand the motion in your mind's eye, you will recognize the solution (hopefully).
  17. Mar 19, 2007 #16
    fyi, i was right,
    the equation has to do with fnet = ma
    where fnet incorporates magnetic force

    so next time if u dont kno wut ur talking about plz dont answer a question for sum1... instead of saying ok wut u said might make sense u overcomplicate everything
  18. Mar 19, 2007 #17
    My apologies, I was for some reason thinking we were looking for the radius of motion.
    My bad :smile:
    In my opinion, I do not think that the questions I prompted were useless. I still think you should try to understand the motion of the charged object through the B field. :rolleyes:
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