question_answer

A straight section \[PO\] of a circuit lies along the x-axis from \[x=-a/2\]to \[x=+a/2,\]and carries a steady current 'T'. The magnitude of magnetic field due to the section PO at a point to \[y=+a\] will be

A)  Proportional to a      

B)  Proportional to a2

C)  Proportional to I/a     

D)  Equal to zero

Correct Answer: C

Solution :

 \[B=\frac{{{\mu }_{0}}}{4\pi }\frac{I}{a}(\sin \theta +\sin \theta )=\frac{{{\mu }_{0}}I\sin \theta }{2\pi a}\]B at any point on Y axis is inversely proportional to a.