Question
What is an electromagnet? How can you make a simple electromagnet? Describe its properties and list at least four uses.
Solution — Step by Step
An electromagnet is a temporary magnet created by passing electric current through a coil of wire. Unlike a permanent magnet (which retains magnetism), an electromagnet is magnetic only when current flows. When the current is switched off, it loses its magnetic properties.
The magnetic effect of electric current was discovered by Hans Christian Oersted in 1820, who noticed that a compass needle deflected when placed near a current-carrying wire.
Materials needed:
- An iron nail (or iron bolt)
- Copper wire (insulated, about 30–40 cm)
- A battery (1.5V or 3V)
- Switch
- A handful of small iron pins/nails to test the magnet
Steps:
- Take the iron nail — this is the core (iron is used because it is a soft magnetic material, easily magnetised and demagnetised)
- Wind the insulated copper wire tightly around the nail in close loops — each loop is called a turn. Wind in one direction only (no reversals)
- Connect the two ends of the wire to a battery through a switch
- When you close the switch and current flows, the nail becomes magnetic
- Test by bringing the tip of the nail near small iron pins — they will stick to it
- Open the switch — pins fall off (magnet deactivated)
Three factors control how strong the electromagnet is:
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Number of turns: More turns around the core → stronger magnetic field (more loops reinforce the magnetic effect)
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Current through the wire: Higher current → stronger magnet. Current is increased by using a battery of higher voltage (with the resistance remaining the same)
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Core material: Iron core makes the electromagnet much stronger than air core. Soft iron is best because it magnetises and demagnetises easily. Steel is NOT used — it would become a permanent magnet and not switch off
- Switchable: Magnetic effect present only when current flows — useful for on/off control
- Controllable strength: Current can be varied to vary magnetic force
- Polarity reversible: Reversing current direction reverses the poles (N becomes S and vice versa)
- Temporary: Made from soft iron, so easily demagnetised when current is off
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Electric bells: An electromagnet repeatedly attracts and releases a striker against a bell — creates ringing sound
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Cranes in scrap yards: Powerful electromagnets lift heavy iron/steel objects. When magnet is switched off, objects are released at the desired location
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Electric motors: Electromagnets create rotating magnetic fields that drive the motor shaft
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Loudspeakers and headphones: Electromagnets interact with permanent magnets to vibrate a cone/diaphragm, producing sound
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Magnetic Resonance Imaging (MRI) machines: Uses very powerful electromagnets to create magnetic fields for medical imaging
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Electromagnetic locks: Hold doors shut when current flows; release when current is cut (for emergency exits)
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Sorting scrap metal: Separates magnetic metals (iron, steel) from non-magnetic ones in recycling plants
Why This Works
When electric current flows through a wire, it creates a circular magnetic field around the wire (right-hand rule: curl the right hand around the wire, thumb pointing in current direction, fingers show field direction). When the wire is wound into a coil, the magnetic fields from each loop reinforce each other inside the coil, producing a much stronger, linear magnetic field — like a bar magnet.
Inserting an iron core amplifies this effect: the iron core gets magnetised by the coil’s field, and the iron’s own magnetism adds to the external field, increasing the total strength significantly.
Alternative Method
You can also make an electromagnet using a pencil (graphite conducts electricity) as the core, but soft iron gives a much stronger effect because iron has high magnetic permeability.
For CBSE Class 7 exams, know the difference between a permanent magnet and an electromagnet in a table format (3 differences). Also know why soft iron is used for the core (easily magnetised AND demagnetised) and not hard steel (stays permanently magnetised — you can’t turn it off).
Common Mistake
Students often write that copper is used as the core of an electromagnet. This is wrong — copper is non-magnetic and is used for the wire (because it’s a good conductor). The core is iron. Confusing the roles of iron (core = amplifies magnetism) and copper (wire = carries current) is a classic error.