A current of 5 A is flowing from South to North in a straight wire. Find the magnetic field due to a 1cm piece of wire at a point 1 m North-East from the piece of wire.
Here, I = 5A , dl = 1 cm = 0.01 m , r = 1m , θ = 45°
dB = ${ µ}_{ 0 }$/ 4$\pi$ . Idl sin θ / ${{r}^{2}}$
= ${{10}^{-7}}$ x 5 x 0.01 x sin 45° / 1 x 1
= 3.54 x ${{10}^{-9}}$ T
Its direction is vertically downwards.