question_answer

Three infinitely long wires are placed equally apart on the circumference of a circle of radius a, perpendicular to its plane. Two of the wires carry current I each, in the same direction, while the third carries current 2I along the direction oppo- site to the other two. The magnitude of the magnetic indution \[\overset{\to }{\mathop{B}}\,\] at a distance r from the centre of the circle, for r > a, is 

A) 0

B) \[\frac{2{{\mu }_{0}}}{\pi }\frac{I}{r}\]

C) \[-\frac{2{{\mu }_{0}}}{\pi }\frac{I}{r}\]

D) \[\frac{2{{\mu }_{0}}}{\pi }\frac{Ia}{{{r}^{2}}}\]