Physlet Illustration: Magnetic Field of a Straight Wire

 

 

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In this simulation, a single, straight wire is oriented perpendicular to the plane of the screen. It carries a current that runs into (or out of) the screen. A compass (whose needle points "north") may be dragged around in the plane of the screen. Can you map the lines of the magnetic field caused by the current-carrying wire? Use the radio buttons to change the direction of the current and see how it affects the field.

Hints:

  1. Like magnetic poles repel and unlike poles attract.
  2. The arrow end on the compass needle is a "north seeking" (or simply a "north") pole.
  3. Magnetic field lines begin on north poles and end on south poles and show, at any point along the line, the direction of the force that would be experienced by a north pole.
  4. What, then, is the connection between the compass and the field lines?
  5. What are the shapes of the field lines in the vicinity of the wire?
  6. How does the current direction affect the direction of the field lines? (Remember the right-hand rule.)

Reference

See Walker, Section 22-6

Illustration written by Steve Mellema