Electromagnetism

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Hans Christian Oersted showed this in April 1820 when a current-carrying wire deflected a compass needle. This proved that electric current produces a magnetic field.

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A compass needle placed under a wire deflected when electric current was switched on. This showed that current creates magnetic effects around the wire.

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It showed that electricity and magnetism are connected. This opened the way for devices like the dynamo, electric motor, radio, television, and fiber optics.

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A magnetic field is the region around a magnet or current-carrying conductor where magnetic force can act without physical contact.

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Field lines are crowded where the field is strong and spread apart where the field is weak. Near the poles, the magnetic field is strongest, so the lines are closer together.

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A compass placed at any point on the field line settles along the tangent. The tangent at that point gives the direction of the magnetic field.

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Magnetic flux is the number of magnetic field lines passing through a plane area perpendicular to the field. Its SI unit is weber.

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Magnetic flux density is magnetic flux passing through unit area taken perpendicular to the field. It is also called magnetic field induction. Its unit is tesla.