ii$)$ A flat, circular disk with radius $2$ meters lies in the $xy-$plane centred at the origin $)=(0.$ The charge density on the surface is described by ${}_s={}^{2}cos\frac{O}{n}\frac{C}{m^2},$ where $$ is the radial distance from the origin and $\frac{O}{?}$ is the azimuthal angle $)\frac{O}{?}(2.($Note: azimuthal angle $\frac{O}{?}$ exist in cylindrical coordinates system.$)$