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For more information, please see full course syllabus of AP Physics B
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Force on a Current in a Magnetic Field

  • A magnetic field exerts a force on a wire carrying current. If the wire is straight, the force is given by F = I L x B, where I is the current, L is a vector whose magnitude is the length of the wire, and whose direction is that of the current, and B is the magnetic field vector.
  • A magnetic field also exerts a torque, on a current loop, given by I A B sin(theta), where I is the current in the loop, A is the loop area, B is the magnitude of the magnetic field, and theta is the angle between the magnetic field vector and the normal (perpendicular) to the plane of the loop.

Force on a Current in a Magnetic Field

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Effect of Magnetic Field on Current 0:44
    • Conduction Wire, Horse Shoe Magnet
    • Introducing a Battery to the Wire
    • Wire Bends Pushing Left
    • Wire Bends Toward Right
    • In Absence of Magnetic Field
    • Magnet and Wire Force Towards Upward
  • Force 11:55
    • Conductor Connected to Battery, Carrying Current to Right
    • Magnetic Field Oriented into Page
    • Force on 1 Change
    • Total Force on Wire
    • Vector of magnitude
    • Direction is Scalar
    • Force on Wire
  • Torque on a Current loop 35:38
    • Square of Rectangle of Wire in Loop
    • Passing Current
    • Force on 1
    • Force on 3
    • Force on 2
    • Force on 4
  • Example 49:33
    • Wire of Length
    • Magnetic Field, Force on Wire
  • Extra Example 1: Lifting a Wire
  • Extra Example 2: Rod on Two Rails
  • Extra Example 3: Rod on Two Rails with Friction