(bjSketch the Fermi surfaces at Fermi-energies of E, = -0.95, E- =0.0, and E = 0.95. For each Fermi-surface indicate if it would be easier to use an electron or hole description of the electrical carrier conduction (c) For each Fermi-surface mark the points where the line y. = q intersects the Fermi-surface and indicate the direction of the Fermi-velocity at these points. (d) Using the same parameters expand E( q) around the two points in the first Brillouin zone where an effective- mass approximation (in both the q and g. directions simultaneously ) is useful. There are actually four points but I only want you to consider the points where the effective mass matrix is proportional to the identity matrix so that the diagonal elements have the same sign. HINT: One expansion point will have a positive effective mass, and one will have a negative effective mass. Do these look similar or different to the same Fermi-energies in part (b)