(a) The relation, between the angle of incidence :(i) and the corresponding , angle of deviation `(delta)` , for a certain optical decice, is represented by the graph shown in the figure. Identify this device. Draw a ray diagram for this device and use it for obtaining and expression for the refractive index of the material of this device in terms of an angle characteristic of the device and the angle, marked as `delta_m`, in the graph.
(b) Based on Huuygen's construction , draw the shape of a plane wavefront as it gets refracted on passing through a convex lens.