THERE ARE TWO INFINITE LONG PARALLEL RODS .CURRENT I THROUGH 1ST ROD FLOWS FROM TOP TO BOTTOM AND SAME CURRENT I IN THE OTHER ROD FROM BOTTOM TO TOP.A POINT P LIES AT A DISTANCE r FROM SECOND ROD.IF THE SEPARATION BETWWEN THE RODS IS r metre,FIND MAGNETIC FIELD AT Q? Now i hav got the answer to the problem by subtracting the two magnetic fields due to rod 1 and 2.But still i m confused why did we take the minus sign ,i mean why do we need to subtract in this case and not simply add the two like we do if the pint would have been in betwwen the rods...Please try to explain me in little simpler language.

THERE ARE TWO INFINITE LONG PARALLEL RODS .CURRENT I THROUGH 1ST ROD FLOWS FROM TOP TO BOTTOM  AND SAME CURRENT I IN THE OTHER ROD FROM BOTTOM TO TOP.A POINT P LIES AT A DISTANCE r FROM SECOND ROD.IF THE SEPARATION BETWWEN THE RODS IS r metre,FIND MAGNETIC FIELD AT Q?

 

 

Now i hav got the answer to the problem by subtracting the two magnetic fields due to rod 1 and 2.But still i m confused why did we take the minus sign ,i mean why do we need to subtract in this case and not simply add the two like we do if the pint would have been in betwwen the rods...Please try to explain me in little simpler language.