Uses of Electromagnets

This lesson covers the practical applications of electromagnets and compares them with permanent magnets — as required by the Edexcel GCSE Physics specification (1PH0), Topic 8: Magnetism and Electromagnetism. You need to understand why electromagnets are chosen over permanent magnets for specific tasks, and be able to describe how they work in various devices.

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Advantages of Electromagnets Over Permanent Magnets

The key advantage of an electromagnet is that it can be controlled:

Feature	Electromagnet	Permanent Magnet
Switch on/off	Yes — by switching the current	No — always magnetic
Vary strength	Yes — by changing the current	No — fixed strength
Reverse polarity	Yes — by reversing the current	No — fixed poles
Very strong fields	Possible (with high current and many turns)	Limited by material
Power needed	Yes — requires electricity	No — no power supply needed
Demagnetises?	When current is off	No (unless heated or dropped)

Exam Tip: When an exam question asks you to compare electromagnets and permanent magnets, always structure your answer around the three key controllable features: can be switched on/off, strength can be varied, and polarity can be reversed. These are the reasons electromagnets are preferred in many applications.

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Application 1: Relay Switches

A relay is a switch that uses a small current to control a circuit with a large current. This allows you to safely switch high-power devices using low-power control circuits.

How a Relay Works

1. A small current flows through the coil of an electromagnet in the control circuit.
2. The electromagnet becomes magnetised and attracts a soft iron armature (a pivoted lever).
3. The armature moves, closing (or opening) the contacts in the high-power circuit.
4. A large current now flows through the high-power circuit, powering the device (e.g. a motor, heater, or starter motor).
5. When the small current is switched off, the electromagnet demagnetises, a spring pulls the armature back, and the high-power circuit is broken.

Why Use a Relay?

• The operator only handles the low-voltage control circuit — safe from high currents.
• The small current never directly contacts the high-power circuit.
• Common uses: car starter motors, industrial machinery, central heating systems.

graph TD
    A["Small Current<br/>(control circuit)"] --> B["Electromagnet<br/>energised"]
    B --> C["Iron Armature<br/>attracted"]
    C --> D["Contacts Close<br/>(high-power circuit)"]
    D --> E["Large Current Flows<br/>(powers device)"]

    F["Small Current OFF"] --> G["Electromagnet<br/>demagnetised"]
    G --> H["Spring Returns<br/>Armature"]
    H --> I["Contacts Open<br/>(circuit broken)"]

    style A fill:#2980b9,color:#fff
    style B fill:#e67e22,color:#fff
    style C fill:#95a5a6,color:#fff
    style D fill:#27ae60,color:#fff
    style E fill:#c0392b,color:#fff
    style F fill:#2980b9,color:#fff
    style G fill:#e67e22,color:#fff
    style H fill:#95a5a6,color:#fff
    style I fill:#e74c3c,color:#fff

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Application 2: Circuit Breakers

A circuit breaker is a safety device that automatically breaks (disconnects) a circuit when the current becomes too high, preventing damage or fire.

How an Electromagnetic Circuit Breaker Works

1. Current flows through an electromagnet inside the circuit breaker.
2. Under normal conditions, the electromagnet is too weak to operate the switch — the circuit remains complete.
3. If the current exceeds a safe level (due to a fault or overload), the electromagnet becomes strong enough to attract an iron latch.
4. The latch moves, releasing a spring-loaded switch that opens the circuit.
5. Current stops flowing — the circuit and connected appliances are protected.
6. The circuit breaker can be reset by pushing the switch back (unlike a fuse, which must be replaced).

Advantages Over Fuses

Feature	Circuit Breaker	Fuse
Reusable	Yes — can be reset	No — must be replaced
Speed	Very fast response	Slightly slower
Convenience	Easy to reset	Must find correct replacement

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Application 3: Electric Bells

The electric bell is a classic example of an electromagnet application:

How an Electric Bell Works

1. Pressing the bell push completes the circuit.
2. Current flows through the coil — the electromagnet is energised.
3. The electromagnet attracts the soft iron armature.
4. The armature moves towards the electromagnet, and the hammer (attached to the armature) strikes the bell (gong).
5. The armature's movement breaks the circuit at a contact point (the armature pulls away from the contact screw).
6. With the circuit broken, the electromagnet demagnetises.
7. A spring pulls the armature back to its original position, remaking the circuit.
8. The whole process repeats rapidly, producing a continuous ringing sound.

Why an Electromagnet Is Essential

• The bell needs to switch on and off rapidly — a permanent magnet would just pull the armature once and hold it.
• The electromagnet's ability to magnetise and demagnetise quickly is what creates the repeated striking action.

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Application 4: Magnetic Locks

Magnetic locks (maglocks) use electromagnets to secure doors:

• A powerful electromagnet is mounted on the door frame.
• A steel plate (armature) is mounted on the door.
• When the electromagnet is energised, it holds the steel plate firmly — the door is locked.
• To unlock the door, the current is switched off — the electromagnet demagnetises and the door can be opened.
• In an emergency (power failure), the lock automatically releases — this is a safety feature (fail-safe design).

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Application 5: Scrapyard Cranes

As mentioned in an earlier lesson, scrapyard cranes use large electromagnets:

• The electromagnet is suspended from a crane.
• It is switched on to pick up iron and steel scrap (magnetic materials).
• It is positioned over the sorting area and switched off to drop the scrap.
• This would be impossible with a permanent magnet — you could pick up the scrap but not release it.

Key Point

Only iron and steel objects can be picked up. Non-magnetic metals like aluminium and copper are not affected and must be sorted by other methods.

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Application 6: Maglev Trains

Magnetic levitation (maglev) trains use powerful electromagnets to levitate above the track:

• Electromagnets on the train and in the track create magnetic fields that repel each other.
• This lifts the train above the track — there is no physical contact and therefore no friction between the train and the track.
• Other electromagnets propel the train forward by alternating attraction and repulsion along the track.
• Maglev trains can reach very high speeds because there is no friction from contact with rails.
• The electromagnets must be precisely controlled — this requires sophisticated computer systems.

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Choosing the Right Type of Magnet

When deciding whether to use an electromagnet or a permanent magnet, consider: