Which of the following relations represent Biot-Savart's law?

Options

A. `d vec(B) = (mu_(0))/(4pi) I (d vec(l) xx vec( r))/(r )`
B. `d vec(B)= (mu_(0))/(4pi) I (d vec(l) xx vec(r ))/(r^(2))`
C. `d vec(B) = (mu_(0))/(4pi) I (d vec(l) xx vec(r ))/(r^(3))`
D. `d vec(B) = (mu_(0))/(4pi) I (d vec(l) xx vec(r ))/(r^(4))`

Answer

C

Explanation

Biot-Savart.s law states that the magnetic field `d vec(B)` due to an element `d vec(l)` carrying a steady current I at a point P at a distance r from the current element is `d vec(B) = (mu_(0))/(4pi) I (d vec(l) xx vev(r ))/(r^(3))`