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A magnetic field of 0.0200 T [up] is created in a region...

  1. Jan 31, 2017 #1
    1. The problem statement, all variables and given/known data
    A magnetic field of 0.0200 T [up] is created in a region

    Find the initial magnetic force on an electron initially moving at 5.00 X 10^6 m/s [N] in the field.

    2. Relevant equations
    Work clarification and I would like to ask a question in relation to the direction of FM.

    3. The attempt at a solution
    My answer,
    FM=(1.6*10^(-19) C)(5.00*10^6 m/s)(0.0200 T)
    FM=1.6 x 10^-14 N

    Since it is an ELECTRON, it would alter the direction of velocity, changing it from NORTH to SOUTH . With that said, Magnetic field is [UP], Velocity is [SOUTH] and FM is [WEST]. Therefore my final answer is FM=1.6 x 10^-14 N [WEST].


    [Is my answer right?]


    I'm unsure of my answer (Above.) as I was told from 2 of my classmates that I did it wrong. They said that an ELECTRON changes both Velocity's and Magnetic field's direction. However, I looked at the examples my teacher did and he only changed Velocity's direction.


    So I was just wondering who's approach is right, my friends or mine?
     
  2. jcsd
  3. Jan 31, 2017 #2

    gneill

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    Staff: Mentor

    You did fine. The magnetic field is assumed to be externally generated and held constant. Besides, the question is looking for the initial force direction, which means at the first instant the electron encounters the field. So there would be no time for the field to change (which it doesn't, anyways).

    I wonder how your friends handled their changing magnetic field direction? :wideeyed:
     
  4. Jan 31, 2017 #3
    Does anyone else see a problem with using North East and Up coordinates for a magnetic field problem? N and S mean something specific in a magnetic field. I mean I'm sure this is worked correctly due to the statement that the field is "up". However normally if you tell me a particle is moving north in a magnetic field I'm going to think it is traveling along the field lines toward the north magnetic pole. I think this is unnecessarily confusing.
     
  5. Jan 31, 2017 #4

    gneill

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    Staff: Mentor

    So, it's a great case of, "Don't confuse the map for the territory" :smile:

    Magnet polarities were first defined by noting which end of a bar magnet (compass needle) was attracted to and hence pointed towards the geographic north. Of course, that mean that the pole that sits near the geographic pole is really a magnetic south pole...
     
  6. Jan 31, 2017 #5
    Oddly enough, my classmates lost marks for changing the magnetic field. When my teacher asked how they changed the Magnetic field, they simply said "Because of the electron." and my teacher went on to explain how that is not the case. In short, he basically said what you said.

    Thank you so much for reviewing my work and for clarifying the change in direction. I would of thanked you earlier but I was in class. Again thank you!
     
  7. Jan 31, 2017 #6

    gneill

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    Staff: Mentor

    You're welcome. Glad I could help.
     
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