6 11141.03 Question 3 Requirements • 20 cm converging lens and holder • Constructed illuminated object (washer with internal diameter 10 ±1 mm) and crosswires as used in 2011 A2 3 • Screen – plain white paper • Metre rule • 30 cm rule Preparation Illuminated object (washer and cross) construction. Measure the height H of the centre of the lens, mounted in the lens holder above the surface of the bench. Take a sheet of stiff card and use a sharp knife to cut a square aperture of side 40 mm so that the centre of the square is a distance H from the marked edge of the card. The width W of the card depends on the dimensions of the lens holder. Cut a piece of tracing or greaseproof paper about 60 mm square. In the centre of this square use a fi ne felt tip pen ( or similar) to mark an “X” with the arms at least 10 mm long. Place the washer over the “X” so that the intersection of the arms is at the centre of the circular hole in the washer. Using transparent self-adhesive tape, attach the washer to the tracing paper. Avoid covering any part of the hole in the washer. Place the tracing paper on the card so that the washer is at the centre of the 40 mm square aperture, with the washer inside the opening. Tape the tracing paper to the cardboard. The completed object is illustrated in Fig 3.1 Fig. 3.1 Washer and “X” object (not to scale) Place apparatus at workstation. Check that the magnifi cation of the object is approximately 2 when the object distance is 30 cm. Action at Changeover Dismantle all apparatus and leave as at start of experiment.