The magnetic field `dvecB` due to a small current element `dvecl` at a distance `vecr` and element carrying current `i` is,

Options

A. `dvecB = (mu_(0))/(4pi) ((dvecl xx vecr)/( r))`
B. `dvecB = (mu_(0))/(4pi) ""i^(2) ((dvecl xx vecr)/( r))`
C. `dvecB = (mu_(0))/(4pi) ""i^(2) ((d vecl xx vecr)/( r^(2)))`
D. `dvecB = (mu_(0))/(4pi) ""i((dvecl xx vecr)/(r^(3)))`

Answer

D

Explanation

`dB = (mu_(0))/(4pi) . (i(dvecl sin theta))/(r^(2)) = (mu_(0))/(4pi) (i(dvecl xx vecr))/(r^(3))`