O-LevelPhysicsLight5054/32 · May/June 2023 · Q314 Marks

In this experiment you will investigate the image formed by a converging lens. You are provided with: • a converging lens in a lens holder • a metre rule • a 30 cm ruler • a white screen • a triangular object in a piece of white card • a lamp with a power supply to illuminate the triangular object. Set up the apparatus as shown in Fig. 3.1. [Figure 3.1]

(a)Measure and record the height H of the triangular object provided. H = cm[1]
(b)Switch on the lamp and place the lens a distance u = 20.0 cm from the triangular object. Adjust the position of the screen until a sharp, focussed image of the triangular object is formed on the screen.
(b)(i)Measure the height h of the image on the screen. h =[1]
(b)(ii)Calculate the value of 1/h. Give your answer to 2 significant figures. 1/h = [1]
(c)Repeat (b) for values of u between u = 25.0 cm and u = 50.0 cm. Record all your readings and calculations in Table 3.1. Include your readings from (b). Add appropriate headings with units to each column. [Table 3.1][3]
(d)On the grid provided, plot a graph of 1/h on the y-axis against u on the x-axis. Start both axes from the origin (0, 0). Draw the straight line of best fit. [Grid provided][4]
(e)(i)Calculate the gradient m of your line. Show all working and indicate on the graph the values you use. m =[2]
(e)(ii)Calculate the focal length f of the lens. Use your value of H from (a) and the equation: f = 1 / (mH) f = cm[1]
(f)When measuring the height of the image on the screen, your hand and the ruler may obstruct the light from the object and prevent it from reaching the screen. Suggest one improvement to the apparatus provided to overcome this problem.[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.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] 2.6 ± 0.3 (cm) ;
[1] 6.5-9.5 (cm) ;
[1] (1/their h) to 2 sig figs. ;
[1] all columns with headings and correct units ;
[1] 5 sets of data with u values at least 5 cm apart with correct trend (as u increases, h decreases) ;
[1] Consistent d.p down column for h and consistent (with 1/h in (b)(ii)) sig figs. down 1/h ;
[1] axes labelled, quantity and unit (1 / h on y-axis, u on x-axis) ;
[1] scales linear, not awkward, start from (0, 0) ;
[1] points plotted accurately, to the nearest ½ square ;
[1] thin best-fit straight line ;
[1] Values for two points (only) clearly indicated on the line of the graph, points separated by ≥ ½ the line used ;
[1] gradient correctly calculated using coordinates of two points on the line;
[1] calculation of f correct and f in range 12 to 17 cm ;
[1] Use graph paper or a scale stuck onto the screen / clamp ruler against screen /use translucent screen and measure at the back;

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