Small electromagnets can be used to lift paper clips, but giant electromagnets can be used to lift scrap iron.
Electromagnets are more useful than ordinary magnets because the magnetism can be turned on and off. On and off magnetism ís useful in many things—electric doorbells, telephones, electric motors, and others.
What happens when you hold an electromagnet near some thumbtacks? Try it. Lower the magnet very slowly until you hear a click. The tacks and the magnet víbrate when they strike together. The sound is caused by the vibration.
Disconnect one wire. The thumbtacks fall. Connect the wire again. The thumbtacks strike the magnet. If you did this over and over very quickly, the tacks would go click, click, click, click.
