A direct current "I" flows through a straight conducting filament located between points P? and P?. a) Determine the magnetic vector potential at point P, whose location is specified by the perpendicular distance "?" and the angles ?? and ?? as shown in the figure. Express the magnetic vector potential in terms of "?" and the angles ?? and ??. b) Using the Biot-Savart law determine the magnetic flux density B. What are the difficulties in trying to determine B using the curl of A? c) What would be the expression for B if the wire were infinitely long?