Question

The magnetic induction at a point distance $X$ from the centre, on the axis of a circular current carrying coil is inversely proportional to (if $X>>$ radius of coil)

• A. $X$
• B. $X^2$
• C. $X^3$
• D. $X^{3/2}$

Answer 1

The correct option is C $X^3$

$B=\frac{{\mu }_0\cdot i\cdot a^2}{2(a^2+X^2{)}^{3/2}}$
$\because X>>>a$
$\therefore B=\frac{{\mu }_{0}i{a}^2}{2X^3}$
so $B\alpha \frac{1}{X^3}$