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CURRENT ELECTRICITY


                   Conventional Current
                   Before the idea of free electrons which constitute current in
                   metals, it was thought that current in conductors flows due to
                   the motion of positive charges. Therefore, this convention is
                   still in use. We can understand the concept of conventional
                   current from the following analogies.
                   We know that when the ends of heated copper wire are at
                   different temperatures, heat energy flows from the end at
                   higher temperature to the end at lower temperature. The
                   flow stops when both ends reach the same temperature.
                   Water in a pipe also flows from higher level to the lower level.
                   Similarly,  when  a  conductor  is  connected  to  a  battery,  it
                   pushes charges to flow current from higher potential to the
                   lower potential (Fig. 14.2). The flow of current continues as
                   long as there is a potential difference.
                                          Current direction
                                                V





                                                                                       Physics insight
                                        Flow of free electrons

                                     K        +  V  -                              1 litre  s -1
                    Fig. 14.2: Current flows in a conductor when it is connected to a battery  Pump
                   Conventional current is defined as:
                   Current flowing from positive to negative terminal of a battery
                   due to the flow of positive charges is called conventional current
                                                                                        -  +
                   Conventional  current  produces  the  same  effect  as  the                   -1
                   current  flowing  from  negative  terminal  to  the  positive             1 C   = 1 As
                   terminal due to the flow of negative charges.                 The flow of charge in a circuit is
                                                                                 like the flow of water in a pipe
                   The Measurement of Current                                    except  that  a  return  wire  is
                   How can we come to know that current has been established     needed  in  order  to  have  a
                                                                                 complete conducting path.
                   in the conductor? For this purpose, we use different electrical
                   instruments  which  detect  the  current  in  the  circuit.
                   Galvanometer and ammeter are some common examples of
                   current measuring instruments.


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