Question

A very long straight wire of radius r carries current I. Intensity of magnetic field B at a point, lying at a perpendicular distance 'a' from the axis is $\propto$ ___________.

• A. $a^2$
• B. $1_{/a^2}$
• C. $1_{/a}$
• D. a

Answer 1

The correct option is C $1_{/a}$

Magnetic field due to a very long straight wire at a point lying perpendicular distance $a$ from the axis
$B=\frac{{\mu }_{o}I}{2\pi a}$
$⟹B\propto \frac{1}{a}$
Correct answer is option C.