Question
Thu June 28, 2012 By:
 

we define magnetic field lines by close loops.my question is current carrying wire how does it create magnetic field around and an point source charge is moving,where it is originating and how it form closed loops!

Expert Reply
Thu June 28, 2012
The answer to your first question can is way above scope of your course, it include some relativistic phenomenons. However, i can tell that as an electron moves accross an wire, it has an electric field due to its negative charge. thus as it moves in space/ wire, the electric field through a cross section about that wire fluctuates and according to maxwells equations you can see that a fluctuating electric field generates magnetic field and vice-versa.
 
The answer to your second question is very simple. If the magnetic field line will not make a closed loop, then we can say that those field lines have an origin and an end.
But we know that magnetic monopoles does not exist. Whenever there is a north pole there is always a south pole. Hence they close upon themselves.
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