1. Limited time only! Sign up for a free 30min personal 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!

Period of a Proton's Orbit arount magnetic field

  1. Oct 2, 2014 #1
    1. The problem statement, all variables and given/known data
    A proton moves perpendicular to a magnetic field of .005 T. What is the period of the proton's circular orbit?

    2. Relevant equations
    1. T=2pi/v
    2. FB=qv x B


    3. The attempt at a solution
    I know I need to solve for velocity first so I can use the period equation, but I don't understand how I can do that without being given the force. If I knew the force, I could solve for v using equation 2 and then plug that value in to equation 1 to find the period.
     
  2. jcsd
  3. Oct 2, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What sort of force is associated with circular motion?
    (note: eq. 1 is incorrect.)
     
    Last edited: Oct 2, 2014
  4. Oct 2, 2014 #3
    I always thought it was gravitational force, but I have never done a problem in which I need to find the period of a proton moving around a magnetic field. I can't find any other equations that I can use for the period, as I don't have enough information. Is gravitational force what you are referring to?
     
  5. Oct 2, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

  6. Oct 2, 2014 #5
    Okay so are you saying that I need to solve for the centripetal force, and that will be the force that I use in my equation 2? I'm still confused though, because the centripetal force formula requires me to know the velocity and the radius. I see why it would be a centripetal force, I just don't understand how I would be able to solve for that with the information I am given.
     
  7. Oct 2, 2014 #6

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    How many forces are on the proton?
     
  8. Oct 2, 2014 #7
    I honestly thought it was just the magnetic force, we've never done anything where I needed to know anything other than the magnetic field, velocity, and charge. Does gravity act as a force on a proton? And then you said it is like a centripetal force.
     
  9. Oct 2, 2014 #8

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    The centripetal force applies to circular motion - lots of things go in circles: not just planets.
    In this case, the magnetic force is to the proton what gravity is to the planet.

    There is one force on the proton: that is the magnetic force.
    Because this force makes the proton go in a circle, that force is also the centripetal force.
    So how od you write that out mathematically?
     
    Last edited: Oct 3, 2014
  10. Oct 3, 2014 #9
    FB=qv x B= mv2/r

    Is that right? I would still need the radius to be able to solve this.
     
  11. Oct 3, 2014 #10

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Keep going, maybe it cancels at some moment...

    Remember
     
  12. Oct 3, 2014 #11
    I got it thanks.
     
  13. Oct 4, 2014 #12

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes.
    No you don't.
    You don't know v or r, but you do know v/r (see the correct equation 1).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Period of a Proton's Orbit arount magnetic field
Loading...