A long straight vertical wire carries a current of 4 A upward. Two points P and Q lie on the same horizontal line to the east of the wire at distances 3 cm and 6 cm respectively.
a. (a) State how the strength of the magnetic field produced by the wire varies with the perpendicular distance from the wire.
b. (b) Calculate the ratio of magnetic field strengths BP:BQ at points P and Q.
c. (c) If the magnetic field strength at P is 6×10−5T, determine its value at Q.