Problem 9: A student uses a compass and a current-carrying wire to measure the horizontal component of the magnetic field in the laboratory. (This field includes the magnetic field of the Earth, but it may also be affected by nearby electronic equipment or magnetized materials.) Initially the compass is aligned so that the tip of the red arrow points to 0, magnetic north. A wire is aligned north-south at a distance 7.5 cm directly beneath the compass, as shown. A current is initiated in the wire, and when it is increased to 8.5 A, the compass needle points to 30.. Part (a) Calculate the magnitude of the magnetic field due to the current in the wire, B, in micro-tesla, at the location of the compass. Numeric A numeric value is expected and not an expression. B = T Part (b) What is the direction of the current in the wire? Multiple Choice : 1) The current flows from south to north. The current flows from north to south. 2) 3) The direction of the current may not be deduced. Part (c) Excluding the contribution from the current in the wire, what is the magnitude of the magnetic field in the laboratory, Bo, in micro-tesla, near the compass? Numeric A numeric value is expected and not an expression. Bo= T Part (d) Suppose the current is increased to 12.5 A. Where does the tip of the red needle point now? Enter your answer as an angle, 0, measured in degrees in the range 0 0 < 360. Numeric: A numeric value is expected and not an expression. A =