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Homework Help: Help on a physic 30 question

  1. May 17, 2009 #1
    1. The problem statement, all variables and given/known data

    Hello, i am in physics 30 and my teacher gave our class a worksheet for homework and I am stuck on the last question. Could anyone help me out please? Thanks.

    Here is the question: Show that the units of 2[tex]\pi[/tex]m/ qB are equivalent to seconds.

    How can I get the unit for time (s) from that? what do I have to show?

    2. Relevant equations

    3. The attempt at a solution

    I tried using Fc = Fm but I dont get how 2[tex]\pi[/tex] is used in the equation? Or does it even have an effect and is there just as a constant with no units.
    Last edited: May 17, 2009
  2. jcsd
  3. May 17, 2009 #2
    Welcome dulask :smile: Start by writing out all of the units for each symbol in the expression
    [tex]\frac{2\pi m}{qB}[/tex]

    I do not know what any of them are just by looking at them. I could venture a guess, but I rather not :wink:
  4. May 17, 2009 #3


    User Avatar
    Gold Member

    This problem is kinda annoying as B is in Tesla, q is a charge, m is a mass right? Well here's a nice little trick:

    Do you know the Lorentz force law? F = q(E + v x B)? On one side is a force, something with units you should know and are far more comfortable with. On the other side, it has these crazy coulomb and tesla units! I'll assume you may not have gone over it but basically, dimensionally F = qvB! From there you should be able to figure it out.
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