Iron has a BCC crystal structure; at room temperature, a=2.87A, shear modulus is 78GPa. Use a=1. (a) Calculate the magnitude of the Burgers vector of a perfect dislocation in iron. Give your answer in nm. nm (b) Calculate the shear stress required to make an initially straight section of dislocation line in iron, pinned in place at two points 45nm apart, operate as a Frank-Read source. Give your answer in MPa. MPa