Please Solve in half an hour. (b) A CD player uses a laser diode that emits light of wavelength 780 nm. This is focused

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Please Solve in half an hour.
(b) A CD player uses a laser diode that emits light of
wavelength 780 nm. This is focused precisely onto the surface of
the CD by means of a thin lens of focal length 0.16 mm.
(i) The laser emits from a point 0.21 mm from the lens. Treating
the laser as a point source, calculate the distance between the
lens and the surface of the CD.
(ii) The laser diode is now replaced with one of a shorter
wavelength. The distance from laser to lens is unchanged. Explain
why the distance between lens and CD would be expected to change in
order to maintain focus.
(iii) Assuming that the lens is made of a single element of
material having normal dispersion, would the focal distance
increase or decrease? Explain why.