Loud speaker is a device which converts the electrical energy into the sound energy. But how the loud speaker works? The shape of loudspeaker is like a cone made of plastic. In the middle, the round shaped permanent magnet is fixed which produces fixed electric field. In the middle of magnet there is space where a piece of soft iron core is kept. This iron core is wounded by the wires and it can move.
When the ac current is supplied, the pole of magnet also changes and produces attraction and repulsion force between the magnet and iron. Due to this movement of soft iron core, vibration is produced which results mechanical wave (sound). In this way the loudspeaker sends out sound in all directions.
Now what happens if the loudspeaker is made to work in the reverse way?
Consider the mechanical wave coming from all the direction is focused on loudspeaker. This mechanical wave has a kinetic energy. When the waves strike on the loudspeaker, since the magnet is kept fixed it cannot move but soft iron moves on striking the sound waves. It means the mechanical wave will produce the movement on iron which results the vibration on a loudspeaker. Due to this vibration the core will move inside the magnetic field of round magnet. It means there will be change in magnetic flux, which results, induced current will produce on the wire. That is why there is flow of ac through the wire. In this way we see that reverse phenomena will be helpful to produce electricity. It means that we just need to focus the mechanical waves on the loudspeaker. This mechanical wave will bombard the free iron having the wire wounded around it. Then there will be production of electricity. People are trying to make such device which works in the same manner as discussed above.
Prabin kc
B.Sc. 2nd year
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