question_answer

The magnetic field due to a straight conductor of uniform cross-section of radius a and carrying a steady current is represented by:

A)

B)

C)

D)

Correct Answer: A

Solution :

                The magnetic field at a point outside the straight conductor is given by \[B=\frac{{{\mu }_{0}}i}{2\pi r}\] It means \[B\propto \frac{1}{r}\]                      (if r > a) The magnetic field at a point inside the conductor is \[B=\frac{{{\mu }_{0}}i\times r}{2\pi {{a}^{2}}}\] or        \[B\propto r\]               (if r < a)