A magnetic field describes magnetic influence.
A field describes the direction and strength of magnetic effects in a region. Field lines are a drawing convention; they are not physical strands.
Permanent magnets can produce a field without an external electrical supply. Electromagnets produce a field through electric current.
From a wire to a coil.
Current in a wire produces a magnetic field around it. Winding the wire into a coil combines the effects of successive turns. A suitable magnetic core can strengthen and guide the field.
The result depends on current, turns, geometry and material. Increasing current also increases heating, so “more current” is not an unrestricted improvement.
Turning magnetism into movement.
Energising a suitable coil can attract an iron armature. A spring may return the armature when the coil is de-energised. This is the basic idea behind many relays and solenoids.
A relay uses motion to operate contacts. A solenoid can move a valve or another mechanism. A motor arranges magnetic interaction to produce continuous rotation.
The connection also works the other way.
A changing magnetic flux linked with a circuit induces a voltage. If there is a suitable closed path, that voltage can drive current. This is electromagnetic induction.
A stationary magnet beside a stationary coil does not continuously generate power. The change in linked flux matters.
Recognise the principle in lift equipment.
Contactors use electromagnetic action to operate contacts. Some brakes use an electromagnet to release a spring-applied mechanism. Hydraulic valve coils can move a valve element.
Motor windings produce fields that interact with the rotor. You now have the foundations for studying these components individually before combining them into a lift system.
A closer look
An inductor opposes a change in current by inducing a voltage. Interrupting coil current can therefore create a transient voltage, which suitable circuitry must manage. The amount of stored magnetic energy depends on inductance and current.
Check your understanding
How is an electromagnet different from a permanent magnet?
Reveal the explanation
An electromagnet’s applied field is produced by current in its coil. A permanent magnet does not require that external current. Some core materials can retain residual magnetism after a coil is switched off.