Definition of magnetic field and its effects

Summary

In magnetism and electromagnetism, a magnetic field is a physical property of space that quantifies the magnetic influence at each location. It is responsible for effects such as deflecting moving electric charges (including currents), exerting torques on magnets, and attracting or repelling magnets and magnetized materials. Magnetic fields are produced by moving electric charges (currents) and by magnetized materials, and when they vary with time they can induce electrical currents. Magnetic fields are described mathematically by vector fields. In SI electromagnetism there are two closely related magnetic field quantities: the magnetic flux density B and the magnetic field strength H. ISO defines the magnetic field in terms of H and B, and in vacuum they are related by B = μ0 H, while inside materials they differ because of magnetization. The B-field is commonly defined through its role in the Lorentz force law, which predicts the force on a moving charged particle, and it also determines magnetic forces, torques, and electromagnetic induction. The H-field is useful for calculations involving how currents and magnetized materials contribute to the field, though forces and energy calculations still ultimately require B.

Key Points

• 1

  A magnetic field quantifies magnetic influence at a point and causes forces/torques on magnets and moving charges, and can induce currents when time-varying.

• 2

  Magnetic fields are vector fields; in SI they are represented by B (magnetic flux density) and H (magnetic field strength), with B = μ0 H in vacuum but different behavior inside materials due to magnetization.

• 3

  The B-field can be defined operationally via the Lorentz force law, while the H-field is defined in relation to B and magnetization and is often used to simplify field calculations.