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Overview
A magnetic field is a field that describes magnetic influence around magnets, electric currents, moving charges, and changing electric fields. Magnetic fields affect moving charges and currents and are central to motors, generators, transformers, compasses, speakers, data storage, and electromagnetic waves.
The Field Concept
A magnetic field assigns magnetic direction and strength to points in space. It is commonly represented with field lines.
Magnetic Field Lines
Magnetic field lines form closed loops. Outside a bar magnet, they are often drawn from the north pole toward the south pole.
Sources of Magnetic Fields
Magnetic fields are produced by magnets, electric currents, moving charges, and changing electric fields.
Force on Moving Charges
A moving charge in a magnetic field can experience a magnetic force. The force depends on charge, speed, field strength, and direction of motion relative to the field.
Force on Currents
A current-carrying wire in a magnetic field can experience a force. This principle is used in electric motors and speakers.
Earth's Magnetic Field
Earth has a magnetic field that affects compasses and helps interact with charged particles from space.
Magnetic Materials
Materials respond differently to magnetic fields. Ferromagnetic materials such as iron can become strongly magnetized.
Common Mistakes
A common mistake is thinking magnetic field lines begin and end like electric field lines. Magnetic field lines form loops rather than starting or ending on isolated magnetic charges in ordinary physics.
Why This Matters in Physics
Magnetic fields prepare students for electromagnetism, induction, motors, generators, transformers, waves, and many technologies.