Magnetic Effects
of Electric Current

A magnetic field is the region around a magnet where its force acts. We picture it with field lines: outside a magnet they run from the North pole to the South pole, they are closed loops, and they never intersect.

Oersted noticed a compass deflect near a current — a current produces a magnetic field. Around a straight wire the field is made of concentric circles; its direction follows the right-hand thumb rule (thumb = current, curled fingers = field).

A circular loop concentrates the field; a solenoid (many loops) makes a uniform field inside, behaving like a bar magnet. With a soft-iron core it becomes a strong electromagnet.

Try the interactive at the top of the page — flip the current and watch the field circles and compass needle reverse.

A current-carrying conductor placed in a magnetic field feels a force. Its direction is given by Fleming's left-hand rule: stretch the thumb, forefinger and middle finger at right angles — Forefinger = Field, Middle = Current (Mein Current), Thumb = Thrust (force). The force is largest when the conductor is perpendicular to the field.

An electric motor uses this force on a current-carrying coil to spin — converting electrical energy into mechanical energy. A split-ring commutator flips the current each half-turn so rotation continues.

Faraday discovered the reverse link: a changing magnetic field through a coil induces a current. Move a magnet in or out of a coil and a galvanometer flicks; hold it still and nothing flows. The direction of the induced current follows Fleming's right-hand rule.

An electric generator rotates a coil in a magnetic field to induce current — converting mechanical energy into electrical energy (the opposite of a motor).

Homes receive power through three wires: live (red), neutral (black) and earth (green). Appliances are wired in parallel at 220 V.

• Earth wire — a safety path that carries leakage current from a metal body to the ground, preventing shocks.
• Fuse — a thin wire that melts and breaks the circuit if the current gets dangerously high.
• Short circuit — live and neutral touch directly; resistance collapses and a huge current flows.
• Overloading — too many appliances draw more current than the circuit is rated for.

The whole chapter is one idea seen both ways:

• Current → magnetism: a current makes a field (right-hand thumb rule); a field pushes a current-carrying wire (Fleming's left-hand rule) → the motor.
• Magnetism → current: a changing field induces a current (Fleming's right-hand rule) → the generator.