1. Estimate the minimum crosssection of a copper lead, the source power, and the energy consumption needed to compensate the earth's magnetic eld by means of an electric current. 2. An electron is describing a circular orbit in a magnetic eld in vacuum. On a section of the path, two grids are placed, having a potential difference such that the speed of the electron is changed whenever it passes between them. Under what conditions will the speed increase? You can choose or nd any values that you have to use