GCSE Magnetism & Electromagnetism 🧲

Magnets, motors, generators and transformers — interactive, visual, and with just enough humour to stay awake.

AQA / Edexcel · Electricity meets magnets. Sparks guaranteed.

🧲 Permanent Magnets & Magnetic Fields

Field lines show the direction a north pole would move. They always go N→S outside, never cross.

💬 "Magnetic field lines always go N→S outside the magnet and never cross. If two field lines crossed, a compass would point in two directions at once. Physics says no."

Drag the compass anywhere near the magnet — the needle follows the field direction.

Key rules

Field lines run N→S outside the magnet (S→N inside). Closer lines = stronger field. Lines never cross — if they did, the field would have two directions at one point, which is impossible.

⚗️ Magnetic Materials

Most things don't care about magnets. A select few are obsessed with them.

💬 "Copper thinks it's above magnetism. Aluminium agrees. Iron, nickel and cobalt, however, have no chill whatsoever."

Click a material to see how it responds to a magnet:

Select a material above to test it.

🧲 Hard vs Soft Magnetic

Magnetically soft (iron): easy to magnetise, easy to demagnetise. Perfect for electromagnet cores — turns on and off with the current.

Magnetically hard (steel): hard to magnetise but keeps magnetism once magnetised. Perfect for permanent magnets.

⚡ Ferromagnetic Only

Only iron, nickel and cobalt (and their alloys) are strongly attracted to magnets. These are ferromagnetic.

Paramagnetic materials (aluminium etc.) show tiny, practically unmeasurable attraction. For GCSE, treat them as non-magnetic.

🔌 Electromagnetism — Current Creates a Field

Pass a current through a wire and a magnetic field wraps around it in circles. Oersted discovered this in 1820 by accident.

💬 "Oersted noticed his compass needle twitched when he switched on a nearby circuit. He could have ignored it. He didn't. Electricity and magnetism have been inseparable ever since."

Right-Hand Grip Rule

Point your right thumb in the direction of conventional current. Your curled fingers show the direction of the magnetic field circles around the wire. Reverse current → field circles reverse direction.

Number of turns (solenoid): 5

Current strength: 50%

A straight wire with current has circular magnetic field lines. The field weakens with distance from the wire.

🔧 Electromagnets

A coil + a current + a soft iron core = a magnet you can switch off. Very handy.

💬 "The difference between an electromagnet and a permanent magnet: electromagnets have an off switch. Very useful when you want to put the car down."

Current (A): 3

Number of turns: 5

Core material:

Paperclips lifted

Electromagnet ON

Field strength

Med

Core effect

Iron ×8

Factors affecting electromagnet strength

More turns → stronger field. More current → stronger field. Soft iron core multiplies the field ~8× compared to air core. Cut the current → field disappears instantly (soft iron loses magnetism).

Uses: scrapyard cranes, electric bells, relays, circuit breakers, MRI scanners, maglev trains.

💪 The Motor Effect — F = BIL

A current-carrying wire in a magnetic field experiences a force. This is how every electric motor works.

F = B × I × L

Force (N) = Magnetic flux density (T) × Current (A) × Length of wire in field (m)

Current magnitude (A): 5

Fleming's LEFT Hand Rule (Motor Effect)

Hold your LEFT hand flat:
thuMb = Motion (force direction)
First finger = Field (N→S direction)
seCond finger = Current (conventional current direction)

All three are at 90° to each other.

⚙️ The DC Electric Motor

A rectangular coil + magnets + commutator = continuous rotation. Electrical energy → kinetic energy.

💬 "A motor converts electrical energy to kinetic energy. The commutator is the clever bit — without it, the coil would just wobble back and forth like someone who can't make up their mind."

How the commutator works

The split-ring commutator swaps which brush touches which half of the ring every half-turn. This reverses the current in the coil at exactly the right moment so the force always acts in the same rotational direction. Without it, the coil would reverse and oscillate rather than spin continuously.

Coil

Carries current

Magnets

Provide field

Commutator

Reverses current

Brushes

Transfer current

⚡ Electromagnetic Induction

Move a magnet near a wire, you get electricity. Faraday discovered this in 1831. It powers the world.

💬 "Move a magnet near a wire and you get electricity. This is ALL power generation, everywhere, in all power stations. Moving magnets. Seriously, that's it."

Magnet speed: Medium

Faraday's Law + Lenz's Law

Faraday: Induced EMF ∝ rate of change of magnetic flux. Faster movement = bigger EMF = bigger current.

Lenz's Law: The induced current always opposes the change that caused it (conservation of energy). This is why you feel resistance when pushing a magnet into a coil.

Ways to increase induced EMF

Move the magnet faster · Use a stronger magnet · Use more turns of wire · Use a soft iron core inside the coil

🌀 Generators & Alternators

Spin a coil in a magnetic field → continuously changing flux → continuous AC output.

💬 "Every power station in the world — coal, gas, nuclear, wind, hydro — ultimately works by spinning a coil in a magnetic field. The fuel just heats water to spin turbines. It's all just 'spin the coil.'"

Rotation speed: 1.0×

AC Generator (Alternator)

Uses slip rings — each brush always contacts the same end of the coil. Output is AC (alternating current) — the EMF follows a sine wave.

DC Generator

Uses a commutator (like the motor) — reverses connections every half-turn. Output is pulsating DC — always positive but varies.

🔄 Transformers

Change AC voltage using mutual induction through an iron core. The grid couldn't exist without them.

💬 "Why transmit electricity at 400,000 V? Because P_loss = I²R — high voltage means tiny current means almost no energy lost as heat in the cables. Transformers are the reason your electricity bill isn't astronomical."

Primary turns (n₁): 100

Secondary turns (n₂): 200

Primary voltage V₁ (V): 230

V₁/V₂ = n₁/n₂

V₁×I₁ = V₂×I₂

100% efficient transformer (power in = power out)

Why use high voltage for transmission?

Power loss in cables: P_loss = I²R. Transmitting at high voltage means low current for the same power. Low current → much less I²R heating → much less energy wasted. Transformers step up to ~400 kV at power stations and step down near homes.

✅ Quiz — Test Yourself

5 questions. No peeking at the sections above. (We know you will anyway.)

1. A wire carries current to the right. A magnetic field points vertically downward. Using Fleming's Left Hand Rule, which way does the force on the wire act?

2. A transformer has 200 turns on the primary and 50 turns on the secondary. The primary voltage is 240 V. What is the secondary voltage?

3. Which change would MOST increase the strength of an electromagnet?

4. A magnet is pushed into a coil. The induced current flows clockwise (viewed from the magnet's end). What happens to the induced current when the magnet is pulled OUT?

5. A power station transmits electricity at 400,000 V. Why use such a high voltage rather than the 230 V used in homes?

Key Equations ✕

F = B × I × LMotor effect: Force (N), flux density (T), current (A), length (m)

V₁/V₂ = n₁/n₂Transformer turns ratio = voltage ratio

V₁ × I₁ = V₂ × I₂100% efficient transformer: power in = power out

P_loss = I² × RPower lost as heat in cables (W)

EMF ∝ ΔΦ/ΔtFaraday's law: faster flux change → bigger EMF