Current

The question 'Which came first the chicken or the egg?' can be applied here also because the layperson has a tendency to use the terms current and voltage interchangeably as if both were source of energy it is time to set things straight,



    The applied voltage is the starting mechanism -the current is a reaction to the applied voltage.


In a copper wire sits isolated on a laboratory bench. If we cut the wire with an imaginary perpendicular plane. producing the circular cross section shown in we would be amazed to find that there are free electrons crossing the surface  in both directions. Those free electrons generated at room temperature are in constant motion in random directions, however at any instant of time the number of electrons crossing the imaginary plane in one direction so the net flow in any one direction
is zero. Even though the wire seems dead to the world sitting by itself on the bench, internally , it is quite active. The same  would be true for any other good conductor.



   Now to make this electron flow do work for us we need to give it a direction and be able to control its magnitude. This is accomplished by simply applying a voltage across the wire to force the electrons to move toward the positive terminal of the battery as shown . The instant the wire is placed across the terminals the free electrons in the wire drift toward the positive terminal.


  In total , therefore the applied voltage has established a flow of electrons in a particular direction. In fact by definition,


                        If 6.242x10^18 electrons (1 coulomb) pass through the imaginary plane in 1 second, the flow of charge or current is said to be 1 ampere(A)


The unit of current measurement ampere was chosen to honor the efforts of  andre ampere in the study of electricity in motion using the coulomb asthe unit of charge the current in amperes can be determined using the following equation ,


                                           I= Q/t

                                           I=amperes(A)
                                           Q=coulomb(C)
                                           t= time(s)