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AC AND DC

     


      Do you know, our house bulbs are switched on-off 100 times in one second?  The reason is AC.  Let us explore.

      Take a cell in a remote device.  It supplies a steady 1.5 volt.  Here current flows in only one direction.  That is, the negative electrons flow from negative to positive.  And the conventional current said to flow from positive to negative.  This is what is called direct current or DC.  All chemical batteries, cells supply DC.  And all the electronic devices will only function using DC.
   
     Producing DC is still a costly affair.  Faraday gave us a 'method' (AC) to produce electricity cheaply and easily.

       The method:  " If there is relative motion between a coil of wire and a magnetic field, the electric volt is generated in the coil."

      If a coil is rotated within a magnetic field or magnet rotates within the coil, an electric current start to flow in the coil.  The rotations can be done by a wind flow, rush of water, steam power or by a motor powered by petrol and diesel.  Making mechanical rotations is easy and we can generate megawatts of electrical power.

     But the generated electric current is not steady like DC.  As given in the figure, the voltage increases and decreases repeatedly; the current direction also alternates (+ve, -ve).  Hence it is called alternating current-AC.   Producing and transmitting AC is easy.  Hence we learnt to live with it.  If we transmit AC as it is, there will be heavy loss due to the generation of heat.  Hence, the current is stepped down and the voltage is stepped up using transformers and then AC is transmitted to distant towns and the cities.  This is not easily possible in the case of DC.

      What is shown in the figure is one cycle of AC; if coil rotates 50 times in one second, 50 cycles of AC is produced.  That is the frequency of AC supplied to Indian households.

     Have a close look at the figure.  The voltage touches zero two times in each cycle. That means, our light bulbs and motors are switched off 100 times in one second (50 cycles of AC).  It is so fast, our eyes cannot catch up with this ON-OFF.  Take the mobile camera and take the video of a glowing ordinary bulb in slow motion.  You will be able to observe the flickering when you play back the video.
     Electronic instruments like TV, Computer strictly require DC.  Hence the household AC is converted into DC inside of them.  Remember, we use AC in the plug point to charge DC batteries in the mobile phones.
     Faraday's way of generating AC Electric power is commercially viable and highly successful.  Hence we use it even today.   
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