Electromagnetism
Force on a Current-Carrying Wire
To calculate the force on a current-carrying wire in a magnetic field and explain what affects its size.
What you will learn
Why a wire experiences force in a magnetic field
How current and field strength affect the force
How to calculate force on a straight wire
When the force on a wire is greatest
How to determine the direction of the force
Explanation
For a straight conductor perpendicular to a magnetic field, force is F = BIl. Use magnetic flux density B in tesla, current I in amperes and the wire length l inside the field in metres. The formula applies to the perpendicular arrangement; doubling B, I or l individually doubles the force. Example: A 0.1 m wire is perpendicular to a 0.2 T field and carries 3 A. Calculate force. F = BIl = 0.2 × 3 × 0.1 = 0.06 N. Use only the length within the field. Use clear labels. Give a reason. Use evidence.