question_answer

A straight section PQ of a circuit lies along the X-axis from \[x=-\frac{a}{2}\] to \[x=\frac{a}{2}\] and carries a steady current i. The magnetic field due to the section PQ at a point X = + a  will be                                                         [MP PMT 1987]

A)            Proportional to a                

B)            Proportional to \[{{a}^{2}}\]

C)            Proportional to \[1/a\]    

D)            Zero

Correct Answer: D

Solution :

                   Magnetic field at a point on the axis of a current carrying wire is always zero.