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: Fleming's left-hand rule on charged particles

  1. Nov 1, 2015 #1
    1. The problem statement, all variables and given/known data
    Diagrams (a) to (c) show a magnetic field of flux density 0.2 T directed perpendicularly into the paper. In each of (a) and (b) a conductor of length 0.3 m is entirely within the field and is carrying a current of 4 A in the plane of the paper. In (c) an electron is moving in the plane of the paper at 2 * 106 m/s. Copy the diagrams and show the direction of the force in each case. Also find the magnitude of the forces. (Charge on the electron = 1.6 * 10-19 C.)


    Answers: 96706ca803d9.jpg
    2. The attempt at a solution
    F = BIL sin θ
    F = BQv sin θ

    (a-b) F = 0.2 * 4 * 0.3 * sin 90 = 0.24 N
    (c) F = 0.2 * 1.6 * 10-19 * 2 * 106 * sin 90 = 6.4 * 10-14 N

    The (a-b) graphs we get using the Fleming's left-hand rule. For (c), however, I get the force directed in the opposite direction (to north-east, not south-west). I think this is because (in constrast to (a-b), where there was current in each case and not particle) the particle is directed downwards and thus is negatively charged, so we need to change the middle finger from south-east to north-west. But I'm not sure about that. Any ideas on (c) graph please?
    Last edited: Nov 1, 2015
  2. jcsd
  3. Nov 1, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    If an electron is moving down and to the right, which way is the current?
  4. Nov 2, 2015 #3
    The opposite way, so upwards and left. And having this using the left-hand rule we get the correct answer. Right?
  5. Nov 2, 2015 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted