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CONCEPT SUMMARY

North and south magnetic poles produce magnetic forces.

·        Like poles repel; opposite poles attract.

·        North and south poles always occur in pairs.

Magnetism is a force that acts at a distance and is caused by a magnetic field. The magnetic force strongly attracts an opposite pole of another magnet and repels a like pole. The magnetic field is both similar and different than an electric field.

A magnetic field is produced by the motion of electric charge.

·        In magnetic substances such as iron, the magnetic fields created by spinning electrons do not cancel one another out; large clusters of magnetic atoms align to form magnetic domains.

·        In nonmagnetic substances, electron pairs within the atoms spin in opposite directions; there is no net magnetic field.

An electric current produces a magnetic field.

·        Bending a current-carrying wire into coils intensifies the magnetic field.

·        Placing a piece of iron into a current-carrying coil creates an electromagnet.

A moving charged particle may be deflected by a magnetic field.

·        Deflection is greatest for particles moving perpendicular to the magnetic field, and zero for particles moving parallel to the field.

An electric current is also deflected by a magnetic field.

·        The force is maximum when the current is perpendicular to the field.

Earth itself is a magnet; its magnetic poles are almost 2000 km from its geographic poles.

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