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!

Two particles in a magnetic field

  1. Feb 25, 2005 #1
    Illustration:
    http://home.no.net/erfr1/images/2.jpg
    "A particle, X with mass m and charge q starts with an inital velocity zero, and follows the red path indicated on the drawing. It follows a half circle when entering the magnetic field.

    A new particle, Y with mass m(same) and charge 2q starts from the same place as X. Is the following true og untrue:

    1. The force on Y is double the force on X in the electric field.
    2. The force on Y is double the force on X in the magnetic field.
    3. The time Y uses on the half circle is half the time X uses.

    1. Fex=qE and Fey=2qE. So that's true.
    2. Fmx=qvB = q*sqrt(qU/m) * B.
    And Fmy = qvb = 2q * sqrt(2qU/m) * B. So this statement is false.
    3. I don't get this.

    It's half a circle, so v=Pi*r/T
    And I have tried the formula: v^2/r = 4Pi^2*r / T^2

    But everything I use involves either v, or r og both. And the radius of Y has to be smaller right? Since the mag. force on Y is the biggest. But I don't know the radius! And the speed is such an ugly expression, and I always end up with the square root of an expression, so the difference can't be 1/2.


    The book says that statement 3 is true...

    Please help.

    Thanks
     
  2. jcsd
  3. Feb 25, 2005 #2

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    [tex] T_{X}=\frac{\pi r_{X}}{v_{x}} [/tex] (1)
    [tex] T_{Y}=\frac{\pi r_{Y}}{v_{Y}} [/tex] (2)
    [tex] r=\frac{mv}{qB} [/tex] (3)

    Use (3) for the 2 particles and then combine with (1) & (2) to reach the result.

    Daniel.
     
  4. Feb 25, 2005 #3
    Aaaah! Thank you. So the speed is ruled out and I get:
    Tx= Pi*m/qB
    Ty=1/2 * Pi*m/qB
    Ty=1/2Tx
    I can't believe I spent so much time on this :). Stupid me.

    Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Two particles in a magnetic field
Loading...