Physics
WAEC 2000
- Fix a metre rule on the bench with the graduated face up.
- Place the illuminated object at the zero end of the rule and the screen at the other end as illustrated in the diagram above.
- Measure and record D, the distance between the object and the screen. Evaluate D\(^{2}\).
- Place and move the converging lens between the illuminated object and the screen until a diminished sharp image of the object is formed on the screen. Read and record the position, X\(_{1}\), of the lens. From this position, move the lens towards the object until another sharp image of the object is formed on the screen. Read and record the new position x\(_{2}\), of the lens.
- Evaluate and record L (x\(_{1}\) - x\(_{2}\)), L\(^{2}\)) and (D\(^{2}\) - L\(^{2}\))
- Repeat the procedure for D = 90, 80, 70 and 60 cm. In each case, evaluate, L L\(^{2}\) and (D\(^{2}\) - L\(^{2}\)). Tabulate your readings.
- Plot a graph of D\(^{2}\) - L\(^{2}\) on the vertical axis against D on the horizontal axis.
- Determine the slope, S, of the graph and evaluate K = \(\frac{s}{4}\). State two precautions taken to ensure accurate results.
(b)i. Distinguish between a real image and a virtual image.
Draw a ray diagram to show how a converging lens may be used to form a real diminished image of an object.
Explanation
Table os values/observation
D(cm) |
D\(^{2}\)cm |
X\(_{1}\)(cm) |
X\(_{2}\)(cm) |
L=(x\(_{1}\)-x\(_{2}\))cm |
L\(^{2}\)cm |
D\(^{2}\)-L\(^{2}\)cm |
100 |
10000 |
80.50 |
18.30 |
62.20 |
3868.8 |
6131.16 |
90 |
8100 |
70.20 |
19.00 |
51.20 |
2621.4 |
5478.56 |
80 |
6400 |
59.10 |
20.00 |
39.10 |
1528.8 |
4871.19 |
70 |
4900 |
46.70 |
22.00 |
24.70 |
610.09 |
4289.91 |
60 |
3600 |
29.00 |
7.60 |
21.40 |
457.96 |
3142.04 |
Slope (s) = \(\frac{y_{2}-y_{1}}{x_{2}-x_{1}} = \frac{6000-3000}{100-50} = \frac{300}{50}\) = 60
Evaluate K = \(\frac{8}{4} = \frac{60}{4}\) = 15
Precaution:
- I avoided parallax when reading the metre rule.
- I ensured that a sharp image is formed on the Screen.
(b) Real image is formed by the actual intersection of rays whereas a virtual image is formed by the apparent intersection of rays when their directions have been produced backwards, or a Real image is formed at the front of the mirror while a virtual image is formed at the back of the mirror.
ii
An object beyond 2F, the image is real, inverted, smaller than an object, between F and 2F, ray parallel to the principal axis and ray passes through the optical centre.
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