Uses of Electromagnets

Electromagnets are incredibly versatile because they can be switched on and off. In this lesson you will explore key applications of electromagnets and understand why they are preferred over permanent magnets in many situations. This maps to AQA GCSE Combined Science Trilogy (8464) specification section 6.7.2.

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Why Are Electromagnets Useful?

The key advantage of an electromagnet over a permanent magnet is that an electromagnet can be switched on and off by controlling the current. Its strength can also be varied by changing the current or the number of turns.

Feature	Permanent Magnet	Electromagnet
Switchable	No — always on	Yes — switch on/off with current
Adjustable strength	No — fixed strength	Yes — vary current or turns
Retains magnetism	Yes	Only while current flows
Power source needed	No	Yes — needs a current

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Applications of Electromagnets

1. Scrapyard Crane

A large electromagnet is attached to a crane in a scrapyard.

• Switched on — the electromagnet attracts and lifts iron and steel objects (e.g. car bodies).
• Moved to the desired location.
• Switched off — the objects are released and dropped.

A permanent magnet would not work here because you could not release the load.

2. Electric Bell

An electric bell uses an electromagnet to repeatedly strike a gong:

graph LR
    subgraph "Electric Bell Operation"
        A["Current flows"] --> B["Electromagnet magnetises"]
        B --> C["Attracts iron armature"]
        C --> D["Hammer strikes gong"]
        D --> E["Armature breaks contact"]
        E --> F["Current stops — electromagnet demagnetises"]
        F --> G["Spring pulls armature back"]
        G --> H["Contact remade"]
        H --> A
    end

The bell rings continuously because the make-and-break cycle repeats rapidly.

3. Circuit Breakers (Magnetic Type)

When the current in a circuit becomes dangerously high:

1. The increased current makes the electromagnet stronger.
2. The electromagnet attracts an iron catch, which opens a switch.
3. The circuit is broken, stopping the current flow and preventing overheating or fire.

4. Relay Switches

A relay uses a small current in one circuit to switch on a much larger current in a separate circuit.

1. A small current flows through the electromagnet coil.
2. The electromagnet attracts an iron armature.
3. The armature closes a switch in the second (high-current) circuit.
4. When the small current is switched off, the electromagnet releases the armature and the second circuit opens.

Relays are used in car starter motors, industrial machinery and automated systems.

5. Magnetic Resonance Imaging (MRI) Scanners

MRI scanners in hospitals use very powerful electromagnets (often superconducting) to create detailed images of the inside of the body.

6. Maglev Trains

Magnetic levitation trains use electromagnets to levitate above the track, eliminating friction and allowing very high speeds.

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Choosing Between a Permanent Magnet and an Electromagnet

Requirement	Best Choice	Reason
Needs to be switched on/off	Electromagnet	Can be controlled by current
Needs variable strength	Electromagnet	Vary current or turns
No power supply available	Permanent magnet	Does not need electricity
Constant, reliable field needed	Permanent magnet	Always on, no power failures
Navigation (compass)	Permanent magnet	Small, portable, no power needed

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Worked Example

Q: A scrapyard uses an electromagnet to sort magnetic materials from non-magnetic materials. Explain why an electromagnet is used rather than a permanent magnet.

A: An electromagnet is used because it can be switched on to attract and lift magnetic materials such as iron and steel, and then switched off to release and drop them at the desired location. A permanent magnet could not be switched off, so the materials could not be released easily. Additionally, the strength of the electromagnet can be adjusted by changing the current, allowing it to handle loads of different sizes.

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Common Mistakes

Mistake	Correction
"Electromagnets are always stronger than permanent magnets"	Not necessarily — some permanent magnets (e.g. neodymium) are very strong. The advantage of electromagnets is being switchable
"Electromagnets attract all materials"	They only attract magnetic materials (iron, steel, cobalt, nickel)
"A relay is the same as a circuit breaker"	A relay switches a second circuit on; a circuit breaker opens a circuit for safety

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Summary

• Electromagnets can be switched on and off and their strength can be varied — this is their key advantage.
• Applications include: scrapyard cranes, electric bells, circuit breakers, relays, MRI scanners and maglev trains.
• Choose an electromagnet when you need control over the magnetic field; choose a permanent magnet when you need a constant field without a power supply.

Exam Tip (AQA 8464): In application questions, always state the key advantage — the electromagnet can be switched on and off. If relevant, also mention that its strength can be varied. These are the two points AQA is looking for.

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Scrapyard Crane: A Closer Look

The scrapyard crane is the classic AQA exemplar. A large electromagnet (often more than a metre in diameter) is suspended from a crane jib. When a worker wants to move a pile of scrap steel:

1. The crane lowers the electromagnet onto the pile.
2. A high current is switched on, magnetising the electromagnet strongly.
3. Steel and iron objects are attracted to the electromagnet and lifted.
4. Once the load is above the desired location (e.g. a waste skip), the current is switched off.
5. The electromagnet demagnetises rapidly (soft iron core) and the load drops cleanly.

A permanent magnet would fail at step 5: you could not release the load without physically scraping it off the magnet — inefficient and dangerous. Electromagnets also separate magnetic from non-magnetic materials: aluminium cans, copper piping, plastics and glass fall off because they are unaffected, while iron and steel cling on.

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Electric Bell: Cycle Explained in Detail

The electric bell is an elegant application of make-and-break circuitry:

1. Pressing the button closes the circuit; current flows to the electromagnet.
2. The electromagnet attracts an iron armature (a pivoted lever with a hammer on the end).
3. The hammer strikes the gong, producing a ringing sound.
4. As the armature moves, it breaks a contact in the circuit, cutting the current.
5. With no current, the electromagnet loses its magnetism.
6. A spring pulls the armature back to its rest position.
7. The contact is re-made, current flows, and the cycle repeats — dozens of times per second.