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FROM MOBILE TO TOWER AND BACK

   



    Imagine a positive charge and a negative charge kept at some distance apart.  There is a force of attraction between them.  An invisible electrical line of force connects them.  Hold one charge and oscillate it up and down ( in imagination).  The electrical line oscillates like a rope.  Or we can say, electric field oscillates.  The oscillating electric field creates an oscillating magnetic field(Maxwell's law).  That is, electromagnetic waves are produced by the oscillation of charges. 
     Take two metal rods. Send alternating current through them. Opposite charges oscillate in the rods. Loops of waves are created and moves away.        This process is like the production of  soap bubbles.  For each blow of air, one bubble is created and it flies off.  For each oscillation of the charges, one wave is created and it moves away.
Hence, the oscillating charges create the electromagnetic wave which propagates itself in the space.  If the charges vibrates 1000 times a second, 1000 waves are created per second.  We call it the frequency.

 Tower:    This idea is used in all the antennas.  High frequency alternating current is sent through a loop of wire-Antenna.  Charges oscillate.  Radio waves (electromagnetic waves) are created and spreads out. 

 Mobile:  When the radio waves hit the antenna, varying magnetic field in the wave creates feeble current in the metal antenna(Faraday's law).  It is amplified, then picture , text and sound is extracted by the mobile from the electric current.

     In short, antenna is the device which converts oscillating electric current into electromagnetic waves and vice versa.  
     Invisible little compact antenna is there in the mobile.  Large parabolic antenna is there in the tower.  Waves spread like a light from the top of the tower and the waves are picked up by all the phones in that area.  The signal waves from the phone is picked up by the nearest tower. 
    When you hold the phone, you cannot hide.

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