Kiangsu-Chekiang College (Shatin)

Physics Revision Test (2002-2003)

Name : （ ） Time : 60 minutes

Class : F.3 Marks : / 100

Date : 03-Apr-2003

Answer ALL questions Section A: Multiple-choice questions (30 marks)

1

In the above figure, what is the angle of reflection on mirror M2?

A 40o

B 45o

C 50o

D 55o

B

2 Which of the following correctly describe(s) the nature of an image formed by a plane mirror?

(1) It is behind the mirror.

(2) It is virtual.

(3) It is inverted.

A (1) only

B (1) and (2) only

C (2) and (3) only

D (1), (2) and (3)

B

3 In the following figure, two plane mirrors at right angles face each other. An object is place at O. Multiple images are thus formed by the mirrors. Which of the images CANNOT be observed by the observer?

2

A I2 only

B I3 only

C I2 and I3 only

D I3 and I4 only

D

4 Which of the following statements about refraction of light is/are correct?

(1) A light ray is bent towards normal when it passes from a less dense medium to a denser medium.

(2) The ratio of the angle of incidence to the angle of refraction is constant.

(3) When a light ray passes form one medium to another, it is refracted because the speed of light is different in the two different media.

A (1) only

B (2) only

C (1) and (3) only

D (1), (2) and (3)

C

5 A light ray passes from air into water (refractive index 1.33). What is the smaller angle between the reflected ray and refracted ray?

A 97o

B 105o

C 111o

D 117o

3

C

6 The following figure shows a light ray travelling from medium X to a vacuum. What is the refractive index of medium X?

A )sin (90

sin βθ−°

B )(90sin)(90sin

βθ

−°−°

C βsin

)(90sin

θ−°

D θsinβsin

A

7 A light ray travelling in air hits the face of a rectangular glass block with the angle of incidence 40 . If the refractive index of glass is 1.5, which of the following best represents the path of the light ray?

C

4

8 Which of the following statements about the image formed by a concave lens is/are correct?

(1) It is between the lens and object.

(2) It is always diminished.

(3) It will be formed at infinity if the object is located at the focus of the lens.

A (1) only

B (2) only

C (3) only

D (1), (2) and (3)

B

9 If F and F ' is the foci of a concave lens, which of the following ray diagrams is/are INCORRECT?

(1)

(2)

(3)

A (2) only

B (1) and (3) only

C (2) and (3) only

D (1), (2) and (3)

D

10. Some words are viewed by a lens. The image of the words is shown in the following figure.

5

Which of the following statements is/are correct?

(1) The object is located within one focal length from the lens.

(2) The image is virtual.

(3) The lens is a convex lens.

A (1) only

B (3) only

C (1) and (2) only

D (1), (2) and (3)

D

END OF SECTION A

Section B: Conventional Questions (70 marks) There are SIX questions in this section. Answer ALL questions in this section.

1 Mr Chan, accompanied by his wife and his daughter, Irene, visits a friend. At the entrance of his friend's house, there is a vertical plane mirror.

*(a) Explain, by using appropriate laws in physics, why Mr Chan cannot see the image of his feet when he looks towards the plane mirror. (4 marks)

(b) What image can Mr Chan see most possibly as he looks in the plane mirror? (Head, hands or feet of Mrs Chan, Irene or himself?) (1 mark)

6

Solutions Marks

(a) Since Mr Chan's feet are near the lower right corner of the plane mirror

and the normal of the plane mirror is horizontal, the reflected ray must travel towards the upper left corner of the

plane mirror. (By the laws of reflection.) Mr Chan's eyes are near the upper right corner of the plane

mirror, so he cannot see the image of his feet.

1A

1A1A

1A

(b) Mrs Chan's feet. 1A

2 A light ray travels from medium X to air. The following graph shows the rel ation between sin i and sin r.

(a) Calculate the refractive index of X. (2 marks)

(b) Find the value of i when sin r is maximum. What is the physical meaning of this value of i? (3 marks)

Solutions Marks

(a) Refractive index = isinrsin

graph of slope

1=

4.05.0

=

1M

= 1.25 1A(b) sin r attains its maximum when sin r = 1.0. When this happens,

sin i = 2511.

1M

=> i = 53.1o

This is the critical angle of medium X. 1A1A

3 (a) Karen stands in front of a plane mirror. Her eyes are 3 m from it. (See Figure a.) There is a clock 0.5 m behind her eyes. She sees the image of the clock in the mirror.

7

Figure a

(i) State FOUR properties of the image of the clock as observed by Karen. (4 marks)

(ii) Figure b shows the image of the clock as observed by Karen.

Figure b

What is the time? (1 mark)

(iii) How far is the image of the clock from Karen's eyes? (2 marks)

(b) Karen wants to see the back of her head. Therefore, she arranges two mirrors in two different ways. (See Figure c.)

Figure c

(i) Copy Figure c and complete the path of the ray in each arrangement.

(3 marks)

(ii) Explain which arrangement (A or B) Karen should use. (2 marks)

(c) Karen draws a ray diagram showing the diffuse reflection in her notebook. (See Figure d.)

Figure d

Explain why the ray diagram is incorrect and draw the correct one.

(3 marks)

8

Solutions Marks

(a) (i) Any four of the following (1 mark for each): of the same size as the object virtual laterally inverted upright/erect as far behind the mirror as the object is in front

4 x 1A

(ii) The time is 4:05. (iii) Distance between the image of the clock and the mirror = 3.5 m Distance between the image and Karen's eyes = (3.5 + 3.0) m = 6.5 m

1A

1A

1A (b) (i)

(1 mark for each reflection) 3 x 1A

(ii) In arrangement B, her head blocks the light from her back. 1A Therefore she should use arrangement A. 1A

(c) The angle of reflection is not equal to the angle of incidence in each reflection.

1A

(1 mark for each correct reflected ray) 2 x 1A

4 Jack tries to find out the refractive index of a plastic as follows. He directs a light ray AO to enter the semicircular block made of the plastic. Part of the light is refracted into the air along OE and part of it is reflected along OB. After the experiment, he finds that the refractive index of the plastic is 1.58.

9

*(a) Describe how the set-up could be used to measure the refractive index of the plastic.

(5 marks)

(b) If the angle of incidence θ is 30o, what is the angle of refraction φ?

(2 marks)

(c) Calculate the critical angle of the plastic block. (2 marks)

(d) The angle θ is increased from 0o to 90o. Briefly describe the changes in the refract ed ray OE. (2 marks)

(e) Describe briefly TWO applications of total internal reflection. (4 marks)

Solutions Marks

(a) Measure several sets of readings of φ and θ. Plot a graph of sin φ against sin θ. Fit the best straight line through the points. The slope of the graph is the refractive index of the plastic. (effective communication)

1A 1A 1A 1A 1C

(b) Applying Snell’s law,

°=

=

30sinsin

58.1

sinsinn

φθφ

1M

φ = 52.2o 1A (c) Applying Snell’s law,

critical angle of the plastic block

=

=

−

−

58.11sin

n1sin

1

1

1M

= 39.3o 1A (d) As θ increases, the refracted ray OE turns clockwise. When θ > 39.3o, OE disappears.

1A 1A

(e) The light can be transmitted along an optical fibre by total internal reflection.

Therefore, optical fibre can be used in telecommunication.

1A

1A A glass prism behaves like a perfect mirror when total internal

reflection occurs. Therefore, it can be used as mirrors in periscopes/ binoculars.

1A

1A

10

5 (a) Andy looks at a coin in a bowl of water, as shown in Figure a.

Figure a

(i) Draw a ray diagram to show how Andy views the coin. (1 mark)

(ii) In your diagram, indicate the real depth and apparent depth.

(3 marks)

(b) A light ray hits a 45o-90o-45o plastic prism, as shown in Figure b. The ray splits at T, with one ray travelling along the side TR of the prism and one ray along TU.

Figure b

(i) Explain why there is no bending of the light ray at S and U.

(1 mark)

(ii) Name the phenomenon occurs in the light ray

(1) along STR,

(2) along STU.

(2 marks)

(iii) Draw the normal at T in Figure b. Label the critical angle with the letter C and state its value. (2 marks)

(iv) Calculate the refractive index of the prism. (2 marks)

(c) A periscope consists of two right-angled prisms. Draw a diagram to show the structure of a periscope. In your diagram, draw two light rays passing through the periscope. (4 marks)

Solutions Marks

(a) (i) & (ii)

(correct refracted rays) (correct image of the coin) (correct label of real depth) (correct label of apparent depth)

1A1A1A1A

(b) (i) It is because the light ray enters the prism along the normal. 1A

11

(ii) (1) Refraction. (2) Reflection.

1A1A

(iii)

(correct normal and labels of C) C = 45o

1A1A

(iv) Refractive index

°=

=

45sin1Csin

1

1M

= 1.41 1A(c)

(1 mark for correct position of each prism) (1 mark for each correct light ray)

2 x 1A2 x 1A

6 (a) Johnny and Jenny go to a lake this Sunday. Jenny dives in the lake while Johnny stays on the shore for sightseeing. (See Figure a.)

Figure a

(i) Draw a ray diagram to show how Johnny sees Jenny. Draw on the diagram the image of Jenny's eye. (2 marks)

(ii) Does Jenny appear further away or nearer than she really is?

(1 mark)

(iii) Draw a ray diagram to show how Jenny sees Johnny. Draw on the diagram the image of Johnny. (2 marks)

(iv) Does Johnny appear further away or nearer than he really is?

(1 mark)

12

(b) Jenny's eyes are 5 m below the water surface. She can see everything above the water surface but her view is squeezed into a cone of diameter d on the water surface. (See Figure b.) Such view is called a fish-eye view.

Figure b

(i) Calculate the critical angle of water. Take the refractive index of water as 1.33. (2 marks)

(ii) Calculate the diameter d of the cone of view on the surface.

(2 marks)

(iii) Outside the cone, what does the water surface look like? (1 mark)

(iv) Why does Johnny not see any fish-eye view when he stays on the shore to look into the water? (2 marks)

(v) When Johnny throws a stone into the water, Jenny finds the images formed by the water surface distort. Why? (2 marks)

Solutions Marks

(a) (i)

(correct rays) (correct image)

1A 1A

(ii) Nearer. 1A (iii)

(correct rays) (correct image)

1A 1A

(iv) Further away. 1A (b) (i) Applying Snell's law,

critical angle of water

= −n1sin 1

= −

33.11sin 1

1M

13

= 48.8o 1A (ii) d = 2 x 5 x tan C = 2 x 5 x tan 48.8o = 11.4 m

1M

1A (iii) Outside the cone, the surface looks like a mirror. 1A (iv) It is because fish-eye view can be seen only when we look

at things which are in a less dense medium. As Johnny stays in a less dense medium (air) and looks at

things in a denser medium (water), no fish-eye view can be seen.

1A

1A

(v) The water surface becomes rough. Diffuse reflection occurs and image is distorted.

1A 1A

END OF PAPER