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: Electromagnetism, finding current.

  1. Jun 1, 2013 #1
    1. A 35 loop square coil 0.12 m on a side is positioned in a 0.050 T magnetic field. A 0.20 kg
    mass is suspended from one side of the coil as shown in the diagram attached. How much current must pass through the coil in order for the coil to remain horizontal?

    A. 2.3 A
    B. 4.7 A
    C. 9.3 A
    D. 330 A

    2. Relevant equations


    3. The attempt at a solution

    so I=τ/BAN

    I know that BAN is 0.050 x 0.122 x 35 (the information is given). However, I'm having a little trouble finding τ (torque).

    I know that I need to find the forces on the square coil. But since I don't know I (current), I won't be able to find the force with the equation.

    Any help would be greatly appreciated.

    Attached Files:

  2. jcsd
  3. Jun 1, 2013 #2


    User Avatar
    2017 Award

    Staff: Mentor

    The required force is given by the mass. Which torque do you get from the mass?
    The coil has to compensate this with its own torque.
  4. Jun 1, 2013 #3
    That's alright, I finally understand it now.

    τ = Fl = 0.20x9.8x0.06 = 0.1176
  5. Jun 2, 2013 #4


    User Avatar
    2017 Award

    Staff: Mentor

    It would be useful to keep the units everywhere, this gives a direct cross-check for your measurements.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted