How does a Telephone Work?

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Telephone was invented by Alexander Graham Bell in 1876. It transmits speech in the form of electric currents. The mouth piece of a telephone contains a small carbon microphone. The sound waves produced by our voice make a metallic diaphragm vibrate which squeezes the carbon granules of the microphone. An electric current flows through the microphone and the granules vary its strength as we speak. This varying current then flows along wires to the telephone exchange, which sends it on to the other telephone. There it enters a small loudspeaker in the earpiece. The earpiece contains an electromagnet which causes a diaphragm to vibrate as the incoming current varies. This produces the sound of our voice.

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