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Physics questions, chapter 6
Nama / NameKelas / ClassTarikh / Date

Light and Optics

46 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.

Section A: objective questions

14 marks
Choose the best answer for each question.
1

Question 1

What causes light to refract when it moves from one medium to another?
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B
Refraction is caused by the change in speed of light between mediums of different optical densities.
For the teacher: Remembering, low difficulty, standard 6.1.1
Textbook p. 232
2

Question 2

A ray of light travels from air into a glass block at an oblique angle. Which statement is correct?
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C
Glass is optically denser than air, so the speed decreases and the ray bends towards the normal (i > r).
For the teacher: Understanding, low difficulty, standard 6.1.1
Textbook p. 233
3

Question 3

The speed of light in a liquid is 2.0 × 108 m s−1. What is its refractive index? (c = 3.0 × 108 m s−1)
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A
n = c / v = 3.0 × 10⁸ ÷ 2.0 × 10⁸ = 1.5.
For the teacher: Applying, low difficulty, standard 6.1.2
Textbook p. 233
4

Question 4

A ray in air strikes a glass block (n = 1.5) at an angle of incidence of 40°. What is the angle of refraction?
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D
sin r = sin 40° ÷ 1.5 = 0.6428 ÷ 1.5 = 0.4285, so r = 25.4°.
For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 235
5

Question 5

A transparent material has a refractive index of 2.0. What is its critical angle in air?
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B
sin c = 1/n = 1/2.0 = 0.5, so c = 30.0°.
For the teacher: Applying, medium difficulty, standard 6.2.2
Textbook p. 244
6

Question 6

Which conditions are needed for total internal reflection to occur?
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C
Total internal reflection needs light to travel from a denser to a less dense medium and the angle of incidence to be larger than the critical angle.
For the teacher: Remembering, low difficulty, standard 6.2.1
Textbook p. 243
7

Question 7

The table shows the refractive index of four materials.
MaterialRefractive index
Water1.33
Perspex1.50
Crown glass1.52
Diamond2.42
Which material has the smallest critical angle?
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A
n = 1/sin c, so the largest refractive index gives the smallest critical angle. Diamond: c = 24.4°.
For the teacher: Analysing, medium difficulty, standard 6.2.2
Textbook p. 244
8

Question 8

A coin lies at the bottom of a beaker containing water 12.0 cm deep (n = 1.33). At what depth does the coin appear to be, viewed from above?
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D
apparent depth = real depth / n = 12.0 ÷ 1.33 = 9.0 cm.
For the teacher: Applying, medium difficulty, standard 6.1.5
Textbook p. 239
9

Question 9

An object is placed between the optical centre and the focal point of a convex lens. What are the characteristics of the image?
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B
When u < f, a convex lens forms a virtual, upright and magnified image (a magnifying glass).
For the teacher: Remembering, low difficulty, standard 6.3.3
Textbook p. 256
10

Question 10

A convex lens has a focal length of 10 cm. An object is placed 15 cm from the lens. What is the image distance?
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C
1/v = 1/f − 1/u = 1/10 − 1/15 = 1/30, so v = 30 cm.
For the teacher: Applying, medium difficulty, standard 6.4.2
Textbook p. 261
11

Question 11

A convex lens has a focal length of 15 cm. An object 2 cm high is placed 20 cm from the lens. What is the height of the image?
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A
1/v = 1/15 − 1/20 = 1/60, so v = 60 cm. m = v/u = 60/20 = 3, so image height = 3 × 2 = 6 cm.
For the teacher: Applying, medium difficulty, standard 6.3.4
Textbook p. 258
12

Question 12

An astronomical telescope has an objective lens of focal length 80 cm and an eyepiece of focal length 4 cm. What is its magnification at normal adjustment?
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D
M = fo / fe = 80 ÷ 4 = 20.
For the teacher: Applying, medium difficulty, standard 6.5.2
Textbook p. 267
13

Question 13

Why is a convex mirror, not a plane mirror, used as a blind spot mirror at a sharp corner?
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C
A convex mirror gives a much wider field of vision than a plane mirror of the same size (the image is virtual, upright and diminished).
For the teacher: Evaluating, medium difficulty, standard 6.6.2
Textbook p. 276
14

Question 14

A concave mirror has a radius of curvature of 24 cm. What is its focal length?
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B
r = 2f, so f = 24 ÷ 2 = 12 cm.
For the teacher: Understanding, low difficulty, standard 6.6.1
Textbook p. 272

Section B: structured questions

32 marks
Answer all questions. Show your working.
15

Question 15

Diagram 1 shows a ray of light travelling from air into a glass block of refractive index 1.5. The angle of incidence is 60°.
A ray in air strikes the top surface of a glass block at 60 degrees to the normal and bends towards the normal; the angle of refraction is not marked
Diagram 1
[1 mark] (a)Why does the ray bend towards the normal?
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Tick each point you got.
[2 marks] (b)Calculate the angle of refraction.
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Tick each point you got.
[1 mark] (c)Calculate the speed of light in the glass. (c = 3.0 × 108 m s−1)
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Tick each point you got.
For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 235
16

Question 16

Diagram 2 shows three rays of light inside a glass block of refractive index 1.5 striking the glass-air boundary at different angles of incidence.
Three ray diagrams: ray refracted away from the normal, ray along the boundary, and ray totally reflected
Diagram 2
[1 mark] (a)State the meaning of critical angle.
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Tick each point you got.
[2 marks] (b)Calculate the critical angle of the glass.
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[2 marks] (c)A ray strikes the boundary inside the glass at 55°. State what happens to the ray and give a reason.
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[1 mark] (d)Name one natural phenomenon that involves total internal reflection.
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Any 1 points
Tick each point you got.
For the teacher: Analysing, medium difficulty, standard 6.2.1
Textbook p. 243
17

Question 17

An optical fibre has a core of refractive index 1.60 surrounded by cladding of refractive index 1.45.
[2 marks] (a)Explain why the core must have a higher refractive index than the cladding.
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Tick each point you got.
[2 marks] (b)Calculate the critical angle at the core-cladding boundary.
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[1 mark] (c)State one use of optical fibres.
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Any 1 points
Tick each point you got.
For the teacher: Evaluating, high difficulty, standard 6.2.4
Textbook p. 249
18

Question 18

Diagram 3 shows the image of an object formed by a convex lens of focal length 10 cm. The object is 30 cm from the lens.
Ray diagram of a convex lens; the object is 30 cm from the lens and a smaller inverted image forms on the other side
Diagram 3
[3 marks] (a)State three characteristics of the image.
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Tick each point you got.
[2 marks] (b)Calculate the image distance.
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Tick each point you got.
[1 mark] (c)Calculate the linear magnification.
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Tick each point you got.
For the teacher: Understanding, low difficulty, standard 6.3.3
Textbook p. 256
19

Question 19

A magnifying glass is a convex lens of focal length 10 cm. A coin is held 6 cm from the lens, as shown in Diagram 4.
Convex lens with the object inside the focal length; the dashed rays show a larger upright image on the same side as the object
Diagram 4
[2 marks] (a)Use the lens formula to find the image distance. State the sign of your answer.
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Tick each point you got.
[2 marks] (b)State two characteristics of the image.
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Any 2 points
Tick each point you got.
[1 mark] (c)Calculate the linear magnification.
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Tick each point you got.
For the teacher: Applying, high difficulty, standard 6.4.2
Textbook p. 261
20

Question 20

A pupil has three convex lenses of focal lengths 5 cm, 10 cm and 60 cm. She wants to make an astronomical telescope with the largest magnification.
[2 marks] (a)Which lens should be the objective and which the eyepiece? Give a reason.
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Tick each point you got.
[1 mark] (b)How far apart should the lenses be at normal adjustment?
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[1 mark] (c)Calculate the magnification.
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[2 marks] (d)State two characteristics of the final image.
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Any 2 points
Tick each point you got.
For the teacher: Creating, high difficulty, standard 6.5.2
Textbook p. 267