Question

Write down the Biot –Savart law which gives the magnetic field dB at a point P due to current 

element IdL. The vector from the current element to P is r .Sketch a diagram showing the 

relationship between the directions of dB, IdL and r.

Answer 1

$d\vec{B}=\frac{kI[d\vec{l},\vec{r}]}{r^3},$

$dB=\frac{kIdl}{r^2}.$