Page 14 - 1202 Question Bank Physics Form 4

Reinforcement and Assessment of Science Process Skills
for Paper 3 (Practical Test)

1. In this experiment, you will determine the focal length, f of a lens. Carry out the following instructions,
referring to Diagram 1.
D
X wire
screen Lens
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Lamp Screen

u v
i
Diagram 1
(a) Place the centre of the lens at a distance, u = 15.0 cm from the illuminated X wire.

Place the screen close to the lens and move it away from the lens until a sharply-focused image is
formed on the screen.
• Measure the distance, v from the centre of the lens to the screen. Record v in Table 1.
• Calculate uv and record the result in the table.
• Measure and record the distance D from the illuminated X wire to the screen in the table.

(b) Repeat the steps in (a) with the lens at a distance u = 20.0 cm, 25.0 cm, 30.0 cm and 35.0 cm from the
illuminated X wire. Record all the readings in the table. [6 marks]
Table 1

u / cm v / cm uv / cm 2 D / cm
15.0

20.0

25.0
30.0

35.0

(c) Based on the information and observation:
(i) identify the manipulated variable,

(ii) identify the responding variable. [2 marks]
(d) Plot a graph of uv (y-axis) against D (x-axis). Start your axes from the origin (0,0). Draw a best-fit

line. [3 marks]
(e) (i) Based on the graph drawn in (d), determine the value of the focal length of the lens. [2 marks]

(ii) State two precautions that you took in this experiment in order to obtain reliable readings.
[2 marks]

105
Question 1:
SOS TIP (e) Make sure the object, the optical centre of the lens and the centre of the screen were located on the principal axis of the lens. The eye position must be SOS TIP
(b) Make sure that the derived quantities of uv and D must have consistent number of decimal places.
vertically above the scale of the metre rule when taking readings to avoid parallax errors.

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