$2\mathrm{.}7($a$)$ For each of edge, screw and mixed dislocations, cite the relationship between the

direction of the applied shear stress and the direction of dislocation line motion.

Show them in your drawings. $(6$ points$)$

$($b$)$ Consider a metal specimen that has a dislocation density of ${10}^{4}m{m}^{-2}.$ Imagine all

the dislocations in $1000m{m}^3$ were somehow removed and linked end to end. How far

$($in miles$)$ would this chain extended? $(4$ points$)$