The crane magnet
Switch the current ON to lift. Switch it OFF to drop.
Heavy scrap
A scrap yard has heavy iron and steel pieces to lift, move and sort. Tying each piece to a hook would take very long.
What could a crane use to pick up many iron pieces and let them go when needed?
What this lesson covers
The idea
A lifting electromagnet is a strong electromagnet hung from a crane: switching the current ON makes it lift iron or steel objects, and switching it OFF removes the magnetic field and releases them.
Heavy scrap
A scrap yard has heavy iron and steel pieces to lift, move and sort. Tying each piece to a hook would take very long.
What could a crane use to pick up many iron pieces and let them go when needed?
- A strong electromagnet
- A bigger hook
- A bucket of water
Lift and drop
Switch the current ON to lift the scrap. Then switch it OFF.
A magnet you can switch
With the current ON the electromagnet had a magnetic field and held the iron. With the current OFF the field disappeared and the iron fell.
A lifting electromagnet is a strong electromagnet hung from a crane. Current ON: it lifts iron or steel objects. Current OFF: the magnetic field disappears and the objects are released.
- Switch | Magnetic field | Iron and steel objects
- ON | Present | Lifted
- OFF | Gone | Released
Notes
A lifting electromagnet lifts iron and steel when the current is ON. Switch the current OFF and the field disappears, so the objects are released.
Check yourself
The crane operator wants to drop the scrap. The operator …
Where are lifting electromagnets widely used?
When the current is ON, a lifting electromagnet lifts …
Why do the objects fall when the current is switched OFF?
- switches the current ON. With the current ON the magnet keeps holding the scrap.
- switches the current OFF — correct. Yes!
- adds more cells. More current makes the magnet stronger, so it holds on harder.
- Inside wristwatches. They are strong electromagnets for lifting heavy metal items.
- In pencil boxes. They are strong electromagnets for lifting heavy metal items.
- In factories and scrap yards — correct. Yes!
- iron and steel objects — correct. Yes!
- any object, even wood. A magnet attracts magnetic materials like iron and steel.
- only paper. It lifts iron and steel objects.
- The magnet breaks. The magnet is still there. Only its magnetic field disappears.
- The magnetic field disappears — correct. Yes!
- The objects become lighter. They do not become lighter. The magnetic pull stops.