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Very basic magnetism question

  1. Oct 20, 2004 #1
    Another magnetism question

    A particle of mass 7 kg carrying a charge of 82 micro-Coulombs enters a uniform B field of intensity 9 T at a speed 92 m/s and at an angle of 25° with respect to the field lines as shown in the figure. (Positive y is up positive x is right the field is pointing in the positive x direction and positive z is coming out of the screen)


    A) The field does a finite amount of work on the particle as the particle's trajectory is bent by the field.
    B) The x-component of the particle's velocity is unchanged as it passes through the B-Field.
    C) The Force on the particle is in the -z direction.
    D) The particle follows a helical path.
    E) The particle's speed varies as it passes through the B-Field.

    I got these answers:
    A. True Work = Fcos(theta) and theta is always 90 degrees
    B. False magnitude of speed is always the same but direction changes
    C. True - right hand rule
    D. True - Force is negative z direction but acts circularly in the plane of the field
    E. False - Speed can't vary since the force acts perpendicular to the velocity.

    Which ones did I get wrong?
    Last edited by a moderator: Oct 20, 2004
  2. jcsd
  3. Oct 20, 2004 #2
  4. Oct 20, 2004 #3


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    Regarding (A), how can the field do work if the force is perpendicular to the direction of movement?
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