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The wire has length l and carries a current I. A point P is located at a distance lower r from the wire in the x-y plane and perpendicular to the z-axis. The distance of the point from the one end of the current element d I of the wire is upper R. The wire makes an angle theta with the side that joins the point P and the current element of the wire. The angle between the two sides that join the point P and the current element of the wire is d theta. The differential magnetic field induced at the point P is d H. A unit vector at the point P is upper R caret.