A long wire is bent into the shape PQRST as shown in the following figure with QRS being a semicircle with centre O and radius r metre. A current of I ampere flows through it in the direction PQ R S T . Then the magnetic induction at the point O of the figure in vacuum is
magnetic field due to each of half infinite wire is and int he same downward direction and field due to semi circle is also downward and has a value