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Oersted's Discovery


To see how magnetic fields arise out of moving charges or current.


2 m or 3 m section wire; dc power supply capable of about 5 A; large demonstration compass needle.

Procedure and Notes:

Arrange the wire in the air along a N - S line. It may be suspended on ringstand clamps or held by two students. Hold the compass at various locations around the wire (top, bottom, sides) and initiate the current. Observe the deflection of the compass needle.

Summing Up:

Conventional current flowing through a wire produces a magnetic field with field lines forming circles centered on the wire.

The strength of the field lines diminishes with increasing radius. If a strong enough
current is used (greater than 5 A), the needle should point in the direction of the magnetic field as shown on the top and bottom of the wire.

When located at the sides, the compass needle will point north but may dip up or down in response to the field at the side locations. As soon as the current is stopped, the compass needle points north in all locations.