Figure . Coulomb's Law

Mathematically, it is expressed as :

                Q1Q2

        

            F  -------- 

 

                                           d2                     

 

                     Q1Q2

 

    or    = K --------

 

                      d2

    

    In S.I. and M.K.S. system, k = 1/4po. Hence the above equation becomes,

                     

                      

                        Q1Q2

 

          F  =    ----------

                     

                     4pod2

      

Now,      

 

                        1                        1

                      -------- =  -------------        = 8.9878 x 109    = 9 x 109 (approx.)   

                          4po        4p x 8.854 x 10-12 

 

 

Hence, Coulomb's Law can be written as 

            

                               Q1Q2

          F  9 x 109  ----------    newton      --------------   in a medium    

                                       rd2 

 

                                  Q1Q2

             F  =    9 x 109    --------    newton    --------------   in air   

                                            d2 

      

 

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