Solution to Assignment - lpsmc.edu.hkphysics/2010/f3ppt/Solution to Assignment.pdf · ... Join the applications to the appropriate electromagnetic waves. Electromagnetic Wave

S3 / Physics (2010-11) / Assignment / Solution p.1

Chapter 1: Introduction 1. Which of the following is the correct SI unit of length?

A. feet B. inch C. metre D. centi-metre

2. Which of the following symbols represents the correct SI unit of mass?

A. g B. kg C. Kg D. KG

3. Convert the following quantities.

(a) 25 nm = nm000,000,000,1

25 = 2.5 10-8 m

(b) 201 s = s000,000,1

201 = 2.01 10-4 s

(c) 0.72 Mg = (0.72) (1,000,000) = 720,000 g = 7.2 105 g

(d) 612 km = 612,000 m = 6.12 105 m

(e) 34.5 mg = g10000

3451000

5.34 = 0.0345 g

4. Write the following numbers in 3 significant figures.

(a) 1203.2 1200

(b) 8.0456 8.05

(c) 0.2568 0.257

(d) 0.0024518 0.00245

C

B

Solution


Chapter 2: Mathematics for Physics 1. Line A: y = 2x

x 0 1 2

y 0 2 4 Line B: x + 2y = 6

x 0 1 2

y 3 2.5 2 Draw and label the above two straight lines in the graph paper below:

Solution


2. Write down the slope, y-intercept and equation of the straight line. (a)

(b)

The slope of the line is:

slope = 20124

The slope of the line is:

slope = 30103

The y-intercept of the line is:

2 The y-intercept of the line is:

0 The equation of the line is:

y = 2x + 2 The equation of the line is:

y = 3x 4. Find the sin of the following angles. Correct the answers to 3 significant figures.

/ sin

12 0.208 25 0.423 53 0.799

5. Find the sin of the following angles. Correct the answers to 3 significant figures.

sin /

0.123 7.07 0.246 14.2 0.864 59.8

x

y

0

3

1 x

y

0

2

4

1


Chapter 3: Visible and Invisible Light 1. The diagram below lists the rays comprising the electromagnetic spectrum in order of

decreasing frequency. Fill in the blanks A to E.

A : Gamma rays highest frequency

X- rays

B: Ultra-violet rays

C: Visible light

D: Infra-red rays

E: Microwaves

Radio waves lowest frequency 2. Which of the following electromagnetic waves have frequencies higher than that of visible

light? (1) Gamma rays (2) Infra-red rays (3) Microwaves (4) Ultra-violet rays

A. (1) and (2) only B. (1) and (4) only C. (2) and (3) only D. (3) and (4) only

3. Which of the following is a luminous object? (1) Light bulb (2) The sun (3) The moon A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)

Solution

B

A


Chapter 4: Application of Electromagnetic Waves 1. The diagram below shows the electromagnetic spectrum drawn by a student. However,

the order is incorrect.

Low Frequency High Frequency

X-rays Ultra-violet

Rays Radio Waves

Infra-red Rays

MicrowavesGamma

Rays Visible light

(a) Write down the correct order of electromagnetic waves in the boxes below.

Low Frequency High Frequency

Radio Waves Microwaves

Infra-redRays

Visible light

Ultra-violetRays X-rays

GammaRays

(b) Matching: Join the applications to the appropriate electromagnetic waves.

Electromagnetic Wave

Applications

Radio Waves (A) TV broadcasting A To sterilize drinking water E Microwaves (B) To kill the cancer cells G Radar B Infra-red Radiation (C) Checking the banknotes E Remote control C Visible Light (D) To cook in microwave ovens B Radiotherapy G Ultra-violet Radiation (E) To check the bankbook signature E To check weapons hidden in luggage F X-rays (F) Satellite communication B Mobile phone A Gamma Rays (G) Wireless communication between computers A


2. Which of the following electromagnetic waves is most damaging to our body? A. X-ray B. Ultra-violet radiation C. Gamma ray D. Microwaves 3. Which of the following is not an application of ultraviolet radiation? A. Detection of fake banknotes B. Remote control C. Sterilization of drinking water D. checking the bankbook signature 4.

Write down the name of electromagnetic waves involved and its application or phenomenon in the above diagram.

Electromagnet waves Application / Phenomenon in the diagram

Radio waves Radio and TV broadcasting / mobile telephone

Infra-red rays Barbeque, BBQ (heat up food)

Visible light Color spectrum in rainbow

Ultra-violet rays Sunlight

X-rays Medical diagnosis

Gamma rays Kill cancer cells

C

B


Chapter 5: Reflection 1. What is the angle of incidence?

A. 20 B. 70 C. 140 D. 40

2. A ray of light hits a plane mirror as shown in the figure.

What is the angle of reflection?

A. 40 B. 50 C. 80 D. 100 3. Arrange the angle of incidence in the following diagrams in ascending order. (1) (2) (3)

A. (1), (2), (3) B. (1), (3), (2) C. (2), (3), (1) D. (3), (2), (1)

40

20

40 40 90

B

D

B


4. A letter F is placed in front of a plane mirror. What is the shape of image formed?

A.

B.

C.

D.

5. Which of the following graphs correctly shows the relationship between the angle of

incidence (i) and the angle of reflection (r) ?

A. B. C. D. 6. Diffuse reflection occurs when a parallel light beam hits (1) a white paper surface. (2) a polished metal surface. (3) a calm water surface. A. (1) only B. (3) only C. (1) and (3) only D. (2) and (3) only

plane mirror

r

i 0

r

i 0

r

i 0

r

i 0

B

B

A


7. The figure shows a ray of light being reflected by two mirrors successively.

What is the angle of reflection for the final ray? A. 30 B. 60 C. 120 D. 150 8. John stands in front of a plane mirror in which he sees the image of three letters PHY posted

on the wall behind him.

Which of the following is the image he sees?

A.

B.

C.

D.

A

D


Chapter 6: Refraction 1. In an experiment on the laws of refraction, a ray of laser hits a rectangular glass block. The

table below gives a set of results of the experiment. Notes: a and g denote the angles of incidence and refraction.

a 15o 30o 45o 60o 75o g 11o 18o 28o 34o 40o

(a) Is the refracted ray bent towards or away from the normal? (b) Plot a graph of sin a against sin g. (c) Find the refractive index ng of the glass block used in the experiment.

[Solution]

(a) The angle of incidence is larger than the angle of refraction.

Therefore the refracted ray bent towards the normal. (b)

a 15o 30o 45o 60o 75o g 11o 18o 28o 34o 40o

sin a 0.26 0.50 0.71 0.87 0.97

sin g 0.19 0.31 0.47 0.56 0.64

The graph of sin a against sin g is plotted on the following page. (c)

refractive index ng = slope of the graph = (0.9 0) / (0.6 0)

= 1.5


Chapter 7: Refractive Index

1. (a) Calculate the refractive index of X

23.135sin45sin

n

(b) Calculate the angle of refraction.

4.25

5.140sinsin5.1

sin40sin rrr

35

45 air

X

r

40 air

glass (n = 1.5)


(c) Calculate the angle of incidence.

2.34)33.1)(25(sinsin33.125sin

sin iii

(d) Calculate the refractive index of Y.

17.148sin60sin

)4290(sin)3090(sin

n

25

i air

water (n=1.33)

42

30 air

Y


2. A light ray XY pass from air through water and glass as shown.

(a) Draw the refracted ray in each medium in the diagram above. (b) Calculate the angle of refraction of the light ray in each medium.

2.35

576.033.150sinsin

33.1sin

50sinsinsin

r

r

r

nri


Chapter 8: Examples of Refraction 1. A coin is at the bottom of a swimming pool. 2. 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


3. What is its apparent position of the goldfish to the observer in the following figure?

4. The diagram below shows a glass rod put into a beaker of water. Which one is the correct

position of the image of the rod inside water?

B C A

D

glass rod

water

B

D


Chapter 9: Lens 1. The following diagram shows three parallel light rays passing through a lens.

(a) What is the type of the lens (concave or convex) ?

Concave lens ()

(b) What is the focal length ()of the lens?

6 cm


2. Some light rays parallel to the principal axis of a convex lens are shown below. A and B are

the foci of the lens.

(a) Draw the refracted rays in the above diagram.

(b) What is the focal length () of the lens?

12.5 cm


3. As shown in the figure above, the correct combination is

(a) (b)

A. optical centre focal length B. focal length focus C. focus optical centre D. optical centre focus

4. What is the focal length of the convex lens shown above?

A. 4 cm B. 6 cm C. 8 cm D. 12 cm

4 cm

(b)(a)

D

D


Chapter 10: Images Produced by a Convex Lens

1. A ray box is shone on a letter P which is 30 cm away from the convex lens. The image of the letter P is clearly formed on the screen. The focal length of the lens is 20 cm.

(a) State whether the image is real or virtual.

(b) Explain your answer in (a)

(c) A student looks at the screen from X. What is the shape of the image seen?

(d) The student looks at the image from Y. What is the shape of the image seen?


Chapter 11: Ray Diagrams 1. An object O is placed in front of a convex lens. F and F are the foci of the lens. P and Q

are two incident rays. Draw the corresponding refracted rays and find the position of the image.


2. The diagram below shows an object of height 5 cm placed 10 cm in front of a convex lens.

The focal length of the lens is 15 cm. p, q and r and s are four incident rays.


Chapter 12: Linear Magnification of lenses 1.

A student looks through a lens at some musical notes. The notes appear as shown above.

(a) What is the linear magnification of the image?

m = 2

(b) State the nature of the image formed. (real/virtual, erect/inverted, magnified/diminished)

virtual (), erect (), magnified ()

(c) Sketch the ray diagram to show how the image is formed by the lens.


2. Mary carries out an experiment to study the image formed by a convex lens as shown

below. She places an illuminated object P 30 cm in front of the lens and an image is formed on the translucent screen which is 45 cm from the lens.

(a) Sketch the image observed by Mary on the translucent screen.

d (b) Calculate the linear magnification of the image.

m = 45 cm 30 cm = 1.5

(c) State the nature of the image formed (real or virtual; erect or inverted, magnified or diminished).

real (), inverted (), magnified ()


(d) Use a ray diagram to find the focal length of the lens.


3. In the diagram shown, I is the virtual image of object O. Image I is produced by a convex

lens which is not shown in the diagram. The distance between O and I is 10 cm.

(a) What is the magnification of the image?

m = 3 (b) By drawing a suitable light ray, find the position of the lens (L) in the diagram. (c) By drawing another light ray, find the position of the focus (F) of the lens.

(d) Hence, find the focal length of the lens.

f = 7.5 cm

O I


4. In the diagram shown, I is the real image of object O. Image I is produced by a convex lens

which is not shown in the diagram. The distance between O and I is 10 cm.

(a) What is the magnification of the imge?

m = 3 (b) By drawing a suitable light ray, find the position of the lens (L) in the diagram. (c) By drawing another light ray, find the position of the focus (F) of the lens.

(d) Hence, find the focal length of the lens.

f = (7.5 40)(10 cm) = 1.88 cm


Chapter 13: Applications of Convex Lenses

1. An object is placed 4 cm from a magnifying glass of focal length 6 cm.

(a) What kind of lens (convex or concave) is the magnifying glass?

convex lens ()

(b) Complete the ray diagram.

(c) What is the distance of the image from the lens?

12 cm (d) What is the magnification of the image?

m = 3

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Solution to Assignment - lpsmc.edu.hkphysics/2010/f3ppt/Solution to Assignment.pdf · ... Join the applications to the appropriate electromagnetic waves. Electromagnetic Wave