In this experiment, you will find the focal length of a convex lens. You are provided with: • a lamp • a piece of card with a shape cut out to be the illuminated object • a screen • a convex lens • a metre rule. Fig. 3.1 shows the apparatus. The apparatus is set up for you to use. [Figure 3.1] Fig. 3.2 shows the shape of the illuminated object. [Figure 3.2]

1. (a)• Switch on the lamp. • Place the screen a distance D = 60.0 cm from the illuminated object. • Place the lens between the object and the screen so that the lens is about 10 cm away from the illuminated object. • Move the lens slowly away from the illuminated object until a clearly focused image is formed on the screen.
2. (a)(i)Describe two differences between the illuminated object and its image on the screen. 1 ............................................................................................................................................ 2 ............................................................................................................................................[2]
3. (a)(ii)Measure the distance u between the centre of the lens and the illuminated object for D = 60.0 cm. Record your value for u to the nearest 0.1 cm in Table 3.1. [Table 3.1][1]
4. (a)(iii)Deduce the distance v between the centre of the lens and the screen for D = 60.0 cm. Record your value for v to the nearest 0.1 cm in Table 3.1.[1]
5. (a)(iv)Repeat the procedure in the stem of (a), (a)(ii) and (a)(iii) using values of D = 70.0 cm, 80.0 cm, 90.0 cm and 100.0 cm. Record all your values for u and v in Table 3.1.[1]
6. (a)(v)Calculate (u × v) for each value of D and record your answers in Table 3.1. Give your values to 3 significant figures.[2]
7. (b)Use the grid provided in Fig. 3.3 on page 11 to plot a graph of (u × v)/cm² on the y-axis against D/cm on the x-axis. You do not need to start your axes at the origin (0,0). Draw the straight line of best fit.[4]
8. (c)The focal length f of the lens is numerically equal to the gradient of the line. Calculate the gradient of the line. Show all working and indicate on your graph in Fig. 3.3 the values you use. f = .................................................... cm[2]
9. (d)The lens manufacturer states that the focal length of the lens is 15.0 cm ± 10%. Decide, with a calculation, whether your value of f agrees with this statement and tick the box that shows your answer. calculation: ................................................................................................................................................... ................................................................................................................................................... my value for f agrees with the manufacturer's statement my value for f does not agree with the manufacturer's statement.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.