Question

A long-straight wire carries a current and is aligned with the North-South direction. You place a compass 4 cm directly above the wire and above the North/East/South/West plane. The compass needle, which initially pointed North (far away from the wire) is now deflected by 20o from the North direction pointing West. (a)What is the direction of the conventional current? (b) What is the unit vector of the net magnetic field due to the wire and the Earth at the location of the compass? (c) If the Earth’s magnetic field magnitude is 0.05 mT in the plane of the compass and pointing North, then what is the current in the wire?