3.7.5.1
A magnetic field is defined by the force it exerts
Magnetic Fields & Forces — AQA A-Level Physics
Key Definition
Magnetic field — A region of space in which a magnetic pole will experience a force.
- That definition follows the same pattern as electric and gravitational fields. You know a field is there because a test object placed in it feels a force.
- Two things create magnetic fields: moving electric chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)., and permanent magnets.
- Permanent magnets produce their field from aligned electron spins inside the material. At the atomic level, the source is still moving chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)..
- A stationary chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). produces no magnetic field. The charge has to be moving.
- CurrentThe rate of flow of charge. Measured in amperes (A).-carrying wires have magnetic fields around them because currentThe rate of flow of charge. Measured in amperes (A). is moving electrons.
- You can't see a magnetic field, but you can detect it through the force it exerts on magnetic materials like iron.
- Magnetic fields are sometimes called B-fields.
Common Mistake
MEDIUM
Students often: Don't say permanent magnets and moving charges produce 'different types' of magnetic field.
Instead: Both come from moving charge. A permanent magnet's field originates from electron spin. There is one source of magnetic fields: moving charge.
Instead: Both come from moving charge. A permanent magnet's field originates from electron spin. There is one source of magnetic fields: moving charge.