Build an Electromagnet

Why it matters

Scrapyard cranes lift a car, swing it, and DROP it on command. No permanent magnet can let go. The crane's secret is a magnet that exists only while a current agrees to flow.

The idea in plain words

Electromagnet vs permanent magnet. Tap the terms.

soft iron core + N turns + current I

Why does an electric bell use an electromagnet, not a permanent magnet?

The bell's buzz IS the electromagnet switching on and off

• the core: soft iron — magnetises instantly, DE-magnetises instantly when current stops — perfect for on/off
• the contrast: steel — keeps its magnetism — used for PERMANENT magnets, useless for cranes
• the exam list: advantages — switchable, reversible, strength adjustable by current — three wins over permanent magnets
• The hammer must attract and RELEASE many times a second
• Only a switchable magnet can let go

Predict first

To make an electromagnet stronger you can…

Strength ∝ turns × current, multiplied dramatically by a soft-iron core. (Alternate windings cancel!)

• add turns, raise the current, or insert a soft-iron core — correct
• only buy a bigger magnet
• wind the turns in alternating directions

What you do

Lift 12 paperclips — then pull the iron core out and watch your magnet turn feeble.

Check yourself

The best core material for an electromagnet is…

Soft iron amplifies the field AND lets go instantly. Steel would stay magnetised; copper doesn't magnetise at all.

Double the current in the coil and the electromagnet's strength…

Strength grows with N×I — the crane driver's lever is literally a current knob.

Which is NOT a use of electromagnets?

A compass needs a magnet that never switches off — that job belongs to permanent (steel) magnets.

• soft iron — correct
• steel
• copper
• roughly doubles — correct
• is unchanged
• quadruples
• Compass needles — correct
• Scrapyard cranes
• Electric bells and relays