Light and Sound
Thin tungsten filaments inside light globes resist the flow of electrons and heat up to about 2600 degrees Celsius. The globes contain argon gas because the white-hot tungsten would combine with oxygen and burn if exposed to air.
Light can also be produced when an electric current is passed through certain gases and vapours. Electrons flow through sealed glass tubes containing the gas. Electrons associated with the gas are excited and give off electromagnetic radiation. This can either be in the form of visible light or ultra-violet radiation. In the latter case the inside of the glass tube is coated with a chemical substance called a phosphor. This converts the ultra-violet radiation into visible light.
Television is a very important part of modern living. A television system requires a camera and microphone to convert light and sound energy into electrical energy. These electrical signals are converted into radio waves by a transmitter. Our televisions receive these radio waves and convert them back into electrical energy. A beam of electrons is scanned across the inside of the television screen. The energy of the electron beam is converted to light energy as it strikes the phosphor-coated screen. Electrical energy is also converted to sound energy as electrical signals cause vibrations in the loudspeaker.
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