BCIT Physics Department

Demonstration Manual

Electricity and Magnetism

DEM28 - Magnetic Field About a Single Conductor


- To show the direction and the pattern of the magnetic field about a straight current carrying conductor.



The wire unit is focussed on the overhead projector by placing a compass on its surface and adjusting the focus head. Once the focus is established, and the power switched on, iron filings may be sprinkled in the area of the wire to show the magnetic field pattern. The direction of the magnetic field may be shown by moving a (OHP) compass around the single wire.

If you are not using the Overhead Projector place a piece of white printer paper under the apparatus. You will be able to see the pattern created by the iron filings much better.


  1. Tap the unit when sprinkling iron filings, this produces a clearer, circular concentric pattern.

  2. Adjust current to about 2/3 scale on dial.

  3. Magnetic field (and compass direction) can be reversed by turning off the supply and reversing the heavy leads.