The strength of Earth's magnetic field, as measured on the surface, is approximately 6.0 × 10 − 5 T at the poles and 3.0 × 10−5 T at the equator. Suppose an alien from outer space were at the North Pole with a single loop of wire of the same circumference as his space helmet. The diameter of his helmet is 20.0 cm.
The space invader wishes to cancel Earth's magnetic field at his location.
(a) What is the current required to produce a magnetic field (due to the current alone) at the center of his loop of the same size as that of Earth's field at the North Pole?
(b) In what direction does the current circulate in the loop, CW or CCW, as viewed from above, if it is to cancel Earth's field?