Telephone!

2. The number of waves produced within a given period of time. The frequency of a sound wave determines its pitch.
4. The amount of opposition a material has to the flow of electric current through it.
8. An inventor's description of an invention, filed at a patent office so that no other inventor can copy the same invention.
9. The flow of electrons along a conductor, such as a wire.
11. The method of sending light-signals at very high speed through thin glass or plastic tubes bundled together.
13. A device that links a computer to the phone network in the internet.
14. A device containing two substances that react chemically to produce electricity.
15. An electric current that changes strength, and so can produce different effects in a linked apparatus.
17. A rare and expensive metal that is very resistant to corrosion.
18. Science put to practical use, using systems and equipment made by inventors.
19. Vibrations in the air which we, and animals, sense with our ears and hear with our brains.
21. The invisible force that attracts some metals and is given out by an electric current as well as by some substances.
22. A system for changing one kind of information (such as sounds) into another (such as electrical signals).

1. A spacecraft held in orbit around a planet by gravity.
3. A magnet which works only when a current passes through a coil of wire wrapped around an iron core.
5. A substance that allows electricity to flow through it easily.
6. A flexible layer, like a skin, which vibrates in air and in a microphone that can send and receive sound waves.
7. A way of changing continuous electrical current into a sequence of "0" and "1" (on/off) electrical signals.
10. The complete path taken by an electrical current along a suitable conductor.
12. Fast movements, up and down or from side to side.
16. A form of radiation, used to send sounds through the air without wires.
20. A common natural material - coal, charcoal, and diamonds are forms of carbon.