Question

The magnetic field $B$ at a distance $r$ from a long straight wire carrying current varies with distance $r$ as shown in the figure.

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

The magnetic field $B$ at a distance $r$ from a long straight wire carrying current $I$ is given by
$B=\frac{{\mu }_{0}2I}{4\pi r}=\frac{{\mu }_{0}I}{2\pi r}$
$\therefore B\propto \frac{1}{r}$