Radio Marconi – Marconi, an Italian scientist succeeded in inventing a radio, about twenty years after the invention of a telephone. Radio (Fig. 20.3) is such a source of communication in which message is transmitted by electromagnetic waves.
At the studio of radio station when a speaker uses microphone for conversation his voice changes into electrical signals. These signal waves are spread all around by a high antenna. When these waves strike the radio aerial, a weak alternating current of the same particular frequency is produced.
Similarly waves of some other radio stations also produce currents of their own particular frequencies. Tuning circuit fitted in the radio selects the station waves of the choice and strengthens them. This signal reaches the amplifier and then the loudspeaker changes the electric signals again into sound. Thus we hear the sound broadcasted from a place hundreds of kilometer away. Do you know? Radio waves travel with the speed of light.