A circular coil of radius `R` carriers an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance `r` from the centre of the coil, such that `rgt gtR`, varries as

Options

A. `(1)/( r)`
B. `(1)/(r^(3//2))`
C. `(1)/(r^(2))`
D. `(1)/(r^(3))`

Answer

D

Explanation

`B_("axis") = (mu_(0))/(4pi) * (2pi NIR^(2))/(r^(3)) , r gt gt R`
R `to` Radius of loop
`r to ` distance from the centre
`B_("axis") prop (1)/(r^3)`