16 15 The human eye acts as a converging lens system that produces an image on the retina at the back of the eye as shown. front of eye retina Diagram NOT to scale A person with eyesight problems may wear either diverging or converging contact lenses. (a) The diagram below shows an object in front of a converging lens. F is the principal focus. object converging lens F F Determine the position and magnification of the image produced by the lens, by completing a ray diagram. (4) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Magnification = ....................................................... Turn over 17 (b) A short-sighted eye cannot focus on distant objects, because the power of the eye is too great. One student with short sight cannot focus on objects further than 1.5 m without wearing her contact lenses. To view distant objects, it is determined that the combined power of her eye and her contact lens should be 41.7 D. Determine the power and type of lens needed to correct her vision. Assume the equations for thin lens apply to both lenses. distance from eye lens to retina = 2.4 cm (4) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Power = ....................................................... Type of lens ....................................................... (Total for Question 15 = 8 marks) TOTAL FOR SECTION A = 56 MARKS