A D'arsonaval galvanometer has the following data: Flux density $=8{10}^{-3},W\frac{b}{m^2}.$ Number of turns $=300,$ Length of coil $=15mm.$ Width of coil $=30mm,$ Spring constant $=2\mathrm{.}5{10}^{-3}N\frac{m}{r}ad.$ Calculate $($a$)$ the deflection of galvanometer for a current of $1A,$ and $($b$)$ current sensitivity in $m\frac{m}{}A$ if the scale is kept $1m$ away from the mirror.