Which of the following law states that the magnetic field intensity dH produced at a point P, by the differential current element Idl is proportional to the product of Idl and the sine of the angle α between the element and the line joining P to the element and is inversely proportional to the square of the distance R between P and the element?/

A)Ampere's circuit law 
B)Gauss's law 
C)Snell's law 
D)Biot-Savart's law


Answer -D)Biot-Savart's law