All from 2014-16 final exams
Please submit your hardcopy solutions on papers by the end of 22
Feb, Friday.
(1) A lens made of glass (with index of refraction ng = 1.53) is coated witht a thin film of
ITO (with index of refraction ns = 2.00) of thickness t. Visible light of wavelength 450
nm (in air) is incident normally on the coated lens as in Fig. B11.
Fig. B11
(i) Determine the wavelength and frequency of the light in the ITO layer.(2 marks)
(ii) For what minimum value of t will the reflected light be missing? (4 marks)
(iii) Are there other values of t that will minimize the reflected light at this
wavelength? If yes, write down 2 other values of t. If no, explain.
(2 marks)
(2) An object is located 40 cm from the first of two thin converging lenses of focal lengths
20 cm and 10 cm, respectively (Fig. A1). The lenses are separated by 30 cm. Determine
the location and the lateral magnification of the final image formed by the two-lens
system. State whether the final image is upright or inverted.
(5 marks)
Fig. A1
ITO
