1. A hollow cone (like a party hat) has vertex angle 2?, slant height L, and surface charge density ?. It spins around its symmetry axis with angular frequency ?. What is the magnetic field at the tip?
2. At the north magnetic pole the earth's magnetic field is vertical and has a strength of 0.62 gauss/ the earth's field at the surface and further out is approximately that of a central dipole. a) what is the magnitude of the dipole moment in joules/tesla? b) imagine that the source of the field is a current ring on the equator of the earths metallic core. which has a raidus of 3000 km (half of earths radius). how large would the current have to be?