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Homework Help: Direction of Charged particle in magnetic field

  1. Nov 17, 2016 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    F= q v x B

    3. The attempt at a solution

    I tried using the right hand rule to find the direction of the force and seeing if the particle curves that way or not but obviously that's wrong
  2. jcsd
  3. Nov 17, 2016 #2
    Well, if done correctly that is exactly what you want to do. Describe how you applied the right hand rule.
  4. Nov 17, 2016 #3
    well i guess i did something wrong but if i understand correctly. For example for particle 4 , i point my index to the right ( since its going that way) and middle figure towards me since the magnetic field is coming out of the page , thus my thumb is pointing down so particle 4 should be negative right?

    Please tell me if this is right or not I have down to 1 try on my online assignment i can't afford to get this wrong another time

    New Answers :

    Particle 3 is uncharged
    Particle 5 is negative
    Particle 4 is positive
    Particle 2 is positive
    Particle 1 is positive
  5. Nov 17, 2016 #4
    ok, I guess at the end of its motion 4 is moving rightish, and yes, you are pointing all the right directions. V (index finger) X B (middle finger) = thumb. What is thumb? You appear to have leapt from thumb to charge skipping one piece of reasoning. It is a little hard to tell since with only two answers you can easily get the right answer without being right. However I can say that at least one of your answers is wrong.
  6. Nov 17, 2016 #5
    Thumb is the Force, I am pretty sure that particle 1 is positive and particle 3 is uncharged and that particle 4 is negative but what confuses me is particle 2 and particle 5.Btw , what i am doing is seeing if the particle moves in the direction of my thumb(Force) if it doesn't then it is negative and the answers i get are the ones above.I truley have no idea which ones are wrong could you please tell me because i really I don't know where I am messing up the right hand rule. Here is another atempt i notice that i was doing something wrong with the right hand rule please tell me if its correct now.

    Particle 3 is uncharged
    Particle 5 is positive
    Particle 4 is positive
    Particle 2 is negative
    Particle 1 is positive
    Last edited: Nov 17, 2016
  7. Nov 17, 2016 #6
    Exactly, deflecting in the direction of the thumb is positive charge. So what is going wrong? So far you haven't needed me for anything. You knew to apply the right hand rule to find the direction of the cross product. You are using your fingers right. You get that force in the direction of your thumb is positive charge and opposite is negative charge. Yet you are still having a problem. For example I can tell you that particle 1 is not positive.

    Maybe you are just having trouble identifying what direction of force each particle is experiencing. You are supposed to be able to determine that by inspection. Look at the picture and tell me for each particle whether the force acting on the particle is pointed toward the upper left or the lower right.
  8. Nov 18, 2016 #7
    okay so for
    particle 1 : upper left
    particle 2: upper left
    particle 3: is uncharged
    particle 4:lower right
    particle 5 : lower right

    I really don't understand where i'm going wrong , i tried against using the knowledge above and i get

    particle 1 : negative
    particle 2: positive
    particle 3: is uncharged
    particle 4: positive
    particle 5 : negative
  9. Nov 18, 2016 #8


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    Science Advisor
    Homework Helper
    Gold Member

    That's the first set of your answers that is consistent. Particles 1 and 5 curve the their left, so have the same charge, while 2 and 4 curve to their right.
    And I believe all of your answers are now correct.
  10. Nov 18, 2016 #9
    Awww. Beat me to it!
  11. Nov 19, 2016 #10
    thank you very much it was where they were curving that got me messed up a little bit , but when i wrote where they curve it kinda helped.
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