An electron in a periodic lattice has the following energy-wavenumber relationship: E (k) 2m cos (k) a. Plot the E-k diagram (0.5p) b. Determine the effective mass (0.5p) c. Determine the group velocity (0.5p) d. Describe the velocity, direction and effective mass of the electron when a constant electric field (don't confuse with energy in the equation above) is applied from right to left as k varies from - to +. (0.5p)