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!

Homework Help: Electromagnetic problems

  1. Mar 11, 2014 #1
    1. The problem statement, all variables and given/known data

    Let F1,F2 and F3 be the forces experiences by a test charge q at a point in a region of electric and magnetic fields E and B, respectively, for velocities v1,v2 and v3, respectively, of the charge.
    If F1,F2 and F3 are such that A= F1xF2 + F2xF3 + F3xF1 =/= 0, that is, their tips do not lie on a straight line when drawn from a commom point.
    -> Show that B=(1/q)|(F2-F1)/[(v2-v1)xA]|A

    *(The character that Bolded means vector, eg. F1)

    2. Relevant equations
    I think it is related to the Lorentz Force Equation.

    3. The attempt at a solution
    My teacher told us to find the relationship between B and A, which we can assume B=kA and to find k. I don't really have any idea how to work on it as i don't know how to get the direction of each force.
    Please Help me..I am really despair as i have worked on it for a really long time ..
  2. jcsd
  3. Mar 11, 2014 #2


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    Hello Waiyat and welcome to PF.

    Great post. If you use boldface to designate a vector that's good. An alternative is to use ##{\#}{\#}## \ vec F ##{\#}{\#}## to get ##\vec F##.

    I agree. So write it down! Not only for me, but for yourself as well.

    Under 1. I notice you have v1 etc as scalars first, but as vectors later on. And the B is definitely a B

    "teacher told us" is not the same as showing your attempt: you have to start somewhere and get stuck somewhere. Being desperate is not really helpful. Panicking isn't either. Don't worry, help is on the way. Make a first step so potential helpers can see where you are.

    Free advice: make a drawing. Doesn't have to be a prize winner, just a simple diagram. If the problem seems too complicated, draw only a few things you do recognize.
    Last edited: Mar 11, 2014
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted