Electricity & magnetism · Topic 16 of 17

Magnetism & Electromagnetism

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Physics · magnetism

Every magnet has north and south poles; an electric current makes a magnetic field, and a changing magnetic flux through a coil makes a current.

01 · PolesLike poles repel, unlike attract

02 · Current makes a fieldCurrent → magnetic field

03 · InductionChanging flux → induced current

An electric current creates a magnetic field around it must know

Induction: changing magnetic flux through a coil induces current must know

A compass north end points along the magnetic field

Ferromagnetic (strongly magnetic): iron, cobalt, nickel

Electromagnet: coil + current (+ iron core) = magnet you can switch must know

Generator: spinning coil in a magnetic field → electricity (AC)

Transformer: Vs/Vp = Ns/Np; needs AC, not steady DC

Field unit: tesla (T); Earth ≈ 5 × 10⁻⁵ T, MRI ≈ 1.5–3 T

Every magnet has N and S poles; like poles repel, unlike attract must know

Cut a magnet in half → two magnets, each with N and S

Field lines run N → S outside, form loops; closer = stronger

Right-hand rule: thumb = current, curled fingers = field circles

Stronger electromagnet: more current, more turns, iron core

Bigger induced voltage: faster flux change, more coil turns

Commonly confused

	Electromagnetism	Electromagnetic induction
Cause	Current in a wire or coil	Changing magnetic flux through a coil
Effect	Magnetic field around it	Induced voltage and current
Needs change?	No, a steady current works	Yes; no change in flux, no current
Stronger with	More current, more turns, iron core	Faster change, more turns
Devices	Electromagnets, MRI magnets	Generators, transformers

Trap: near Earth's geographic North is a magnetic SOUTH pole

Show 5 more facts

Domains: aligned regions; magnetizing lines them up, heat scrambles them

Lenz's law: induced current opposes the change that made it

Solenoid field B = μ₀nI (n = turns per meter)

Above the Curie temperature (iron 770 °C) no magnetism

All magnetism comes from moving charge (electron spins in magnets)

Pearl

Current makes a magnetic field; a changing magnetic field makes current.

Practice this topic, then test the whole section.

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