The National MagLab is funded by the National Science Foundation and the State of Florida.

Magnetic Field Around a Wire

Whenever current travels through a conductor, a magnetic field is generated.

A magnetic field is created anytime current runs through a conductor. A fact famously stumbled upon by Hans Christian Ørsted around 1820. Magnetic fields have a directional flow. The direction of the field depends on the direction the current is moving.

The tutorial below shows the magnetic fields created by current traveling through a straight wire.

Instructions

1. Notice the how the electrons flow from the negative to positive ends of the wire.
2. Observe the concentric circles around the wire. Those represent the magnetic field lines, and the arrows the direction of that field.
3. Drag the compass needle around the magnetic field. The red end is the north pole.
4. Flip the direction of the current. Watch how the direction of the magnetic field reverses.

The magnetic field moves perpendicular to the current. There is a simple trick used to gauge the direction of a magnetic field created by the current: the right hand rule. According to this rule, if the thumb of the right hand is pointed in the direction of the conventional current, the direction that the fingers curl in order to make a fist (or to wrap around the wire in question) is the direction of the magnetic field.

The shape of the magnetic field depends on the shape of the conductor. When the current travels through a wire the field is circular. The field is strongest closest to the wire, and weakens as you travel outward. A more powerful magnetic field can be achieved when the wire is coiled because it concentrates the field in a smaller space.