(a) What is a wavefront?
(b) (i) State two practical uses of glass prisms.
(ii) List two factors that determine the deviation of a ray of light travelling from air into a triangular glass prism.
(iii) Sketch a graph to illustrate the variation of the angle of deviation d, with that of incidence, i, for a ray of light travelling from air into a triangular glass prism. Indicate on the graph the point at which the angle of incidence equal to the angle of emergence e.

(c) (i) Draw and label a diagram of an astronomical telescope in normal adjustment.
(ii) The angular magnification of an astronomical telescope in normal adjustment is 5. If the focal length of the objective is 100cm, calculate the:
($\alpha$) focal length of the eyepiece;
($\beta$) length of the telescope.


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