Telephone!

3. Vibrations in the air which we, and animals, sense with our ears and hear with our brains.
5. A common natural material - coal, charcoal, and diamonds are forms of carbon.
7. A spacecraft held in orbit around a planet by gravity.
8. A device containing two substances that react chemically to produce electricity.
10. A flexible layer, like a skin, which vibrates in air and in a microphone that can send and receive sound waves.
14. The amount of opposition a material has to the flow of electric current through it.
17. The complete path taken by an electrical current along a suitable conductor.
18. An electric current that changes strength, and so can produce different effects in a linked apparatus.
21. Science put to practical use, using systems and equipment made by inventors.
22. A rare and expensive metal that is very resistant to corrosion.

1. A form of radiation, used to send sounds through the air without wires.
2. The flow of electrons along a conductor, such as a wire.
4. A system for changing one kind of information (such as sounds) into another (such as electrical signals).
6. The invisible force that attracts some metals and is given out by an electric current as well as by some substances.
9. Fast movements, up and down or from side to side.
11. An inventor's description of an invention, filed at a patent office so that no other inventor can copy the same invention.
12. The number of waves produced within a given period of time. The frequency of a sound wave determines its pitch.
13. A way of changing continuous electrical current into a sequence of "0" and "1" (on/off) electrical signals.
15. A magnet which works only when a current passes through a coil of wire wrapped around an iron core.
16. The method of sending light-signals at very high speed through thin glass or plastic tubes bundled together.
19. A substance that allows electricity to flow through it easily.
20. A device that links a computer to the phone network in the internet.