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Page 38

JPN Pahang Physics Module Form 4

Chapter 5 Light

38

a) Based on the graph in Figure 2,

(i) state the relationship between uv and u + v

…………………………………………………………………………………………

[1 mark]

(ii) determine the value of u + v when the value of uv = 400 cm

2

. Show on the graph how

you obtained the value of u + v.

40 cm

From the value of u + v obtained, calculate the image distance, v when u = 20 cm.

20 + v = 40

v = 20 cm

[3 marks]

(iii) calculate the gradient of the graph. Show clearly on the graph how you obtained the

values needed for the calculation.

Gradient = 400/40

= 10 cm

[3 marks]

b) Given that the relationship between u, v and focal length, f of the convex lens used, is

represented by the equation

1 + 1 = 1

u v f

Derive an equation which gives the relationship between uv and (u + v ).

fuv

uv 1

vufuv

[2 marks]

c) Using the equation derived in (b), and the value of gradient calculated in (a)(iii), determine the

focal length of the lens used in the experiment.

The gradient = f

Therefore f = 10 cm

[2 marks]

d) State one precaution taken to ensure the accuracy of the experiment.

………………………………………………………………………………………[1 mark]

uv is directly proportional to (u + v)

The object (lamp), lens and the screen must be arranged in a straight line

perpendicular to the screen

JPN Pahang Physics Module Form 4

Chapter 5 Light

38

a) Based on the graph in Figure 2,

(i) state the relationship between uv and u + v

…………………………………………………………………………………………

[1 mark]

(ii) determine the value of u + v when the value of uv = 400 cm

2

. Show on the graph how

you obtained the value of u + v.

40 cm

From the value of u + v obtained, calculate the image distance, v when u = 20 cm.

20 + v = 40

v = 20 cm

[3 marks]

(iii) calculate the gradient of the graph. Show clearly on the graph how you obtained the

values needed for the calculation.

Gradient = 400/40

= 10 cm

[3 marks]

b) Given that the relationship between u, v and focal length, f of the convex lens used, is

represented by the equation

1 + 1 = 1

u v f

Derive an equation which gives the relationship between uv and (u + v ).

fuv

uv 1

vufuv

[2 marks]

c) Using the equation derived in (b), and the value of gradient calculated in (a)(iii), determine the

focal length of the lens used in the experiment.

The gradient = f

Therefore f = 10 cm

[2 marks]

d) State one precaution taken to ensure the accuracy of the experiment.

………………………………………………………………………………………[1 mark]

uv is directly proportional to (u + v)

The object (lamp), lens and the screen must be arranged in a straight line

perpendicular to the screen