- A magnetic field exerts on a force on a wire (or other conductor) when a current passes through it.
- The general formula for determining the size and direction of the magnetic force on a current-carrying wire involves a complicated integral
- There are several cases in which the solution is relatively easy:
(note that each one involves a cross product of two vectors)
- Straight wire in uniform magnetic field:
F = I (L x B)

- Curved wire in uniform magnetic field:
F = I (L' x B)

where**L'**is a straight vector from the starting point of the wire to its end point - Closed circuit loop in a magnetic field:
F = 0

- Straight wire in uniform magnetic field:
- Although the
**force**on a closed loop of current in a uniform magnetic field is zero, the**torque**is not. - If one defines a special "area vector"
**A,**the magnitude of which is the area of the closed loop, and the direction of which is perpendicular to the plane of the loop (as given by right-hand rule), then the torque on the loop istau = I (A x B)

- The torque acts to make the "area vector" parallel to the direction of the magnetic field
- The
**magnetic moment**"mu" of a closed circuit loop is a vector quantity, the product of its current and "area vector". One can express the torque on a loop astau = mu x B

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Copyright © Michael Richmond. This work is licensed under a Creative Commons License.