15 Turn over 15 A magnifying glass consists of a converging lens and is used to magnify the details of an object. A biologist is studying a flower using a magnifying glass. The anther of the flower has a width of 0.2 mm. The magnifying glass is placed 5.0 cm from the flower and an image of the anther is produced that is 3.5 mm wide. (a) Calculate the power of the lens in the magnifying glass. (5) ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................... Power of lens = ....................................................... 16 (b) The biologist notices coloured fringes around the edges of the image. This is caused by different coloured light being refracted by different angles as it passes through the lens. white light blue red white light red blue The refractive index of red and blue light as the light passes from glass into air can be investigated using a 20° glass prism. white light blue light red light 20° Not to scale A ray of white light is incident along the normal and passes straight into the prism. Blue and red light rays are refracted by different angles as they leave the prism. The angles of refraction are measured using a protractor, like the one shown. 180 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 17 Turn over (i) Deduce whether the measurements made using the protractor are sufficient to measure the difference in the angles of refraction between blue and red light. refractive index of red light in glass = 1.509 refractive index of blue light in glass = 1.517 (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (ii) The angle of incidence at the glass-air interface can be changed by altering the path of the light as it enters the prism. The angle of incidence of the red light at the glass-air interface is changed to 35°. Deduce whether the red light will still be refracted at the glass-air boundary. 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(Total for Question 15 = 11 marks) TOTAL FOR SECTION A = 56 MARKS