1. Not finding help here? Sign up for a free 30min 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!

Force on a wire

  1. Jul 29, 2017 #1
    1. The problem statement, all variables and given/known data
    Screen Shot 2017-07-29 at 6.57.00 pm.png

    2. Relevant equations


    3. The attempt at a solution
    Right hand rule: magnetic field of P on Q is out of the page, and magnetic field of R on Q is also out of the page.
    Left hand rule: Force of P on Q is to the left and R on Q is to the right?

    Please help~ I know this is soooo wrong :(
     
  2. jcsd
  3. Jul 29, 2017 #2

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    What's this left hand rule?
     
  4. Jul 29, 2017 #3
    Fleming's left hand rule...
     
  5. Jul 29, 2017 #4

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Explain how you're applying the rule since you're apparently doing it wrong somehow.

    Also, I've never heard of Fleming's left hand rule.
     
  6. Jul 29, 2017 #5
    So for wire P, magnetic field around it is clockwise, and for wire R, it is anti-clockwise.
     
  7. Jul 29, 2017 #6

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    The field directions you deduced are fine. How did you reason out the direction of the forces?
     
  8. Jul 30, 2017 #7
    for the force of wire P on Q, magnetic field is out of the page, current is down, so force is to the right.
     
  9. Jul 31, 2017 #8

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Rather than using handedness rules, I find it much easier to visualise the field lines.
    If you have currents the same direction along two parallel wires, the field lines run the same way around them, so at a sufficient distance merge to become one system of enveloping lines. The lines like to shrink in length and spread apart from each other, so they pull the wires together.
    With the currents in opposite directions, the two sets of lines run opposite ways around, leading to a bunching up between them. That pushes the wires apart.
     
  10. Jul 31, 2017 #9
    Yes, I understand that.
    So how do I then work out the direction of force on wire Q due to P and R?
    If one attract and the other repel, doesn't that mean the middle wire just stay where it is?
     
  11. Jul 31, 2017 #10

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    If you get pushed on one side and pulled on the other, do you stay where you are?
     
  12. Jul 31, 2017 #11
    No, I don't. OMG I got it. Thank you so much! So the answer is D right?
     
  13. Jul 31, 2017 #12

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes.
     
  14. Jul 31, 2017 #13

    ElectricRay

    User Avatar
    Gold Member

    Thats a nice feeling when you finally got it right? :)
     
  15. Jul 31, 2017 #14
    haha Yeah! It's like discovering a new world :wink::-p
     
  16. Jul 31, 2017 #15

    ElectricRay

    User Avatar
    Gold Member

    It is fun to see that some people give some hints and finaly you get the answer. I agree it is like discovering a new world although it is allready pretty old
     
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: Force on a wire
  1. Wires and Force (Replies: 5)

  2. Force on wire (Replies: 1)

  3. Force between wires (Replies: 1)

Loading...