BCIT Physics Department

Demonstration Manual

Electricity and Magnetism

DEM24.1 - 3D Magnetic Field


- To show the shape of the magnetic field about a cylindrical magnet, in three dimensions.


DEM24.1 - 3D Magnetic Field


The clear block is rotated slowly in all directions to disperse the iron filings in the mineral oil. DO NOT SHAKE THE BLOCK. One cylindrical magnet is centred in the hollow core. The iron filings take the 3-dimensional form of the magnetic field in a short time.


Insert two magnets, with like poles facing. The iron filings show the two like fields repelling the filings (i.e. the two magnetic forces opposing each other).


  1. By viewing the block from one end, one observes the rarely seen 3-dimensional field distribution.

  2. Do not shake the block. It takes a long time for bubbles to be released from the mineral oil.

  3. Do not slide the block on any surface. Scratches prevent the clear viewing of field patterns.

  4. Return the magnets to their holding slots with keepers in place, and the magnets in series loop.

  5. Do not drop or overheat the clear block.

  6. The plastic block is not suited for overhead projection, as depth of field is inadequate and heating may occur

youtube logo Watch a 3D Magnetic Field Demonstration on Youtube video (not produced by BCIT)