In a telephone, our speech is changed into electrical signals. These signals travel through wires, or optical cables that carry them in the form of 
light. The signals can also travel through the air as radio waves, using satellites or antennas. To make a call, you must dial a series of numbers on your telephone. Once the call is connected, the microphone and loudspeaker in the receiver of the phone allows users to talk to each other. The microphone in the mouthpiece produces electrical signals that travel through the wires, or as radio waves. The loudspeaker in the earpiece turns these signals into sounds again
