Magnetic Force on a Current-Carrying Wire

Force on the end-on wire, F = BIL
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Its direction (Fleming's left-hand rule)
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Tilted wire: angle to the field θ
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Tilted wire: F = BIL sinθ
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End-on view: the wire points straight into or out of the page. Tap the wire to reverse its current. To test yourself, untick Show the force, reverse the current or swap the poles, predict the direction of the force, then tick it again to check.
  • ⊙ = current out of the page, ⊗ = current into the page.
  • A stronger magnet (bigger B) is drawn with more field lines, closer together.
  • The field of the magnet (left to right) and the circular field of the current add together.
  • On one side of the wire the two fields point the same way, so the field is stronger (field lines crowded). On the other side they oppose, so the field is weaker.
  • The wire is pushed from the stronger side towards the weaker side.
  • Check with Fleming's left-hand rule: First finger along the Field, seCond finger along the Current, thuMb gives the Motion.
Side view: drag the end of the wire to tilt it in the field.
  • F = BIL sinθ, where θ is the angle between the wire and the field.
  • The force is biggest (F = BIL) when the wire is at 90° to the field, and zero when the wire runs along the field lines.
  • In this view the force points into or out of the page.
  • Notes Example 3: 8.0 cm of wire in a 0.15 T field, carrying 0.45 A at 90° to the field, feels a force of 5.4 × 10-3 N.