Chapter 6 Waves Teacher's Guide 2009

JPN Pahang Teachers’ Guide

Physics Module Form 5 Chapter 6:Wave

CHAPTER 6: WAVE 6.1 Understanding Waves

1. Motion of Waves A wave front is a line or plane on which the vibrations of every point on it are in phase same (same/different) position from the source of the water. and are at the…………. circular 2. When we use a fingertip to touch the surface of water repeatedly, (circular/plane) wave fronts are produced.

3.

Types of waves There are 2 types of waves:Transverse wave (a) ………………. Longitudinal Longitud inal wave (b) ……………….

4. Transverse wave (i). Transverse wave is a wave in which the vibration of particles in the medium is perpendicular perpendicu lar (parallel/perpendicular) to the direction of propagation of the wave. at ……………….. A

A

B

B

crest A = … ………………. (crest / compression) trough B = ………………….. (rarefaction /trough)

(ii). Example of transverse wave: Water wave i. …………………………… …………………………………….. ……….. Light wave ii……………………………………... Electromagnetic Electroma gnetic wave wave iii…………………………………….. 5. Longitudinal waves (i) A longitudinal is a wave in which the vibration of particles in the medium is parallel ………………………. (parallel / proportional) to the direction of propagation of wave. P P

Q

Q

sound wave (ii) Example of longitudinal wave: P = ………………….. compression (crest / compression) Q = ………………….. rarefaction (rarefaction / trough)

1



Amplitude, Period and Frequency of a Wave

A

C

A

B

B C

Figure 6.20 1. Equilibrium 2.

the position of the object where is no resultant force acts on the object. position is …………………………………………………………….

One complete oscillation of the pendulum occurs when the pendulum bob moves from A-B-C-B-A …………............

the time taken to complete an oscillation 3. The period, T of a vibrating system is ……………………………………………... the num number ber o com le lete te osci oscilla llatio tions ns 4. Frequency, f is …………………………………… …………………………………………………… ……………… Hertz (Hz) (Hz) The S.I. unit is …………….. n 1 f = or f = T t 5.

freeze waves patterns on the screen Stroboscope is use to …………………………………….. Stroboscope frequency = number of slits x rotation frequency of stroboscope or f = np

6. Wave speed If the wavelength of the wave is λ , the waves move forward a distance of f x λ per second. Therefore, the speed of waves, v v = f λ

0

0

2



Exercise 6.1

Figure 6.10 A

1. (a)

The wavelength of the wave in the diagram above is given by letter ……….

(b)

D The amplitude of the wave in the diagram above is given by letter …………

2. Indicate the interval which represents one full wavelength.

Figure 6.11 AE, CG, BF, Answer: ……………………

3



Exercise 6.11

1.

In an experiment , Lim observes that a simple pendulum completes 30 oscillations in 15.0 seconds. What is (a) the frequency of oscillation? (b) the period of oscillation? Answer: (a) f = 30/15 = 2 Hz (b) T = 1/f = 1/2 = 0.5 s

2.

Dis Dis lace laceme ment nt/c /cm m 5 0

4

2

6

Time/s

-5 Calculate the frequency of the given wave above. Answer : T = 4s 1 f = Hz T = 0.25 Hz

Dis Dis lace laceme ment nt/c /cm m 5 0 -5 3.

2

4

6 Distance/cm

Based in the displacement-distance displacement-dist ance graph of a wave, find (a) the amplitude (b) the wavelength of the wave Answer: (a) amplitude = 5 cm (b) Wavelength = 4 cm

4


4.


A transverse wave is found to have a distance of 4 cm from a trough to a crest, a frequency of 12 Hz, and a distance of 5 cm from a crest to the nearest trough. Determine the amplitude, period, wavelength and speed of such a wave. Answer: Amplitude: 4/2 = 2 cm

Period: T =

1 f

= 0.08 s

Wavelength: 5 ×2 = 10 cm S eed: f × λ = 120 cm s 5.

-1

A girl moves a long slinky spring at a frequency of 3 Hz to produce a transverse wave with a wavelength of 0.5 m. What is the wave speed of the waves along the slinky spring? Answer: v=fxλ = 3 x 0.5 -1 = 1.5 m s

6.0 cm •

6.

The figure shows a wave front pattern in a ripple tank produced by a vibrating dipper at frequency of 5 Hz. What is the wave speed? Answer: f = 5 Hz λ = 6.0/4 = 1.5 cm V = f λ -1 = 7.5 cm s

5



4.5 cm •

7.

The figure shows a wave front pattern in a ripple tank produced by a vibrating dipper at frequency of 5 Hz. What is the wave speed? Answer: f

= 5 Hz λ = 4.5/3 4.5/3 = 1.5 cm V = f λ -1 = 7.5 cm s

20 cm (5λ) 8.

A mechanical stroboscope has 12 slits and rotates at a frequency 5 Hz. The stroboscope is used to observe water waves. The observer notes there are 6 successive bright bands at a distance 20 cm. cm. Calculate the speed of the water waves. Answer: f=np = 12 x 5 = 60 Hz

9.

λ

= 20/5 = 4 cm V = f λ = 60 x 4 -1 = 240 cm s

The figure shows a loudspeaker produces a sound with a frequency 300 Hz. Calculate (a) the wavelength. (b) the speed of sound Answer: (a) 0.6 m (b) V = f λ = 300 x 0.6 = 180 m s-1

6



5

-1

10. A given given wave travels at a speed of 2 x 10 ms . If the frequency of the wave is 1000 Hz, Calculate the wavelength Answer: λ= v/f 2 x10 5 = = 200 m 1000

11. (a) Base on the figure determine, (i) the amplitude (ii) the wave length -1 (b) What is the frequency of the sound if the speed of sound is 330 ms . Answer: (a) (i) 2 cm (ii) 50 cm (b) f = v / λ = 330 / 0.5 = 660 Hz Damping

Figure 6.12

7



1.

process whereby whereby oscillatio oscillations ns die down due due to a loss loss of energy to friction forces forces . Damping is a …………………………………………………………………………..

2.

increase When a system is damped , the amplitude of the of oscillation ……………. (decreases/increases) slowly until the system stops oscillating.

3.

Damping is usually caused by :(i) external frictional forces such as air resistance (ii) internal forces , where energy is lost from the system in form of heat . Resonance the phenomenon when the oscillating system is driven at its natural frequency A resonance is …………………………… …………………………………………………… ……………………… by a periodic force. …………………………………………………………………………….. Experiment to show a phenomenon of resonance

E A B

D C

Figure 6.12: Barton’s pendulum Pendulum B and D are the same length. When pendulum B oscillates, all the pendulum start to oscillate. But pendulum B and D have the same length, so there have same natural maximum frequency. So pendulum D will oscillate with ……………(maximum/minimum) amplitude.

6.2

ANALYSING REFRLECTION OF WAVES

1.

Reflection of a wave occurs when a wave strikes an obstacle such as barrier, plane reflector, mirror and wall.

2.

The reflection of waves obeys the law of reflection : (i) The angle of incidence is equal to the angle of reflection . ……………………………………………………………… (ii)The incident wave, the reflected wave and the normal lie in the same plane . ………………………………………………………………..

3.

When the reflection of a wave happened , the wavelength , λ , the frequency, f and the do no nott cha chan n e speed, v …………………….but the direction of propagation of the wave changes.

8



Exercise 6.2 Complete the diagram below.

Reflection of water waves

1. Show the pattern of the reflection of the water waves (a)

(b)

(b)

2. Show the dark and bright pattern on the screen below.

Water waves Ri

le tank

Screen B

D

B

D

B

D

B

B = Bright D = Dark

9



Reflection of Light Wave

1. 2.

1.

When rays of light strike any surface the rays are reflected , unless the surface is black, when they are absorbed. A plane mirror is a flat smooth surface which reflects regularly most of the light falling on it.

Figure 6.20 The characteristics characterist ics of reflection of light waves: (i) The size of the image = the size of the object ………………………………………………………………… (ii) The distance of the image = the distance of the object

2. The bright and dark bands of the wave pattern formed on the screen because the convex lens surface of water acts as lenses. The crest of water waves similar with ……………. concave lens (concave lens /convex lens) and the trough of water waves similar with …… (concave lens /convex lens). Exercise 6.21

The diagram shows a single ray of light being directed at a plane mirror. What are the angles of incidence and reflection? (a)

(b)

i

r

o

35

Answer: o i =r = 90 – 55 = 35

i = r = 70 70

10

o


2.


Reflection of sound waves

1. The sound waves are reflected by walls and ceilings of buildings, unborn baby or sea bed.

Figure 6.21 2. The sound wave from the stopwatch experience a reflection after striking the smooth wall. to The angle of incidence, i is equal ………….(equal to /more than/less than) the angle of reflection, r . Exercise 6.22

50 m

1.

The diagram shows a student shouting in front of a school building. Calculate the time taken by the student to hear the echo of his voice. -1 [The speed of sound in air is 340 m s ] Answer: 2s = v x t

,

t=

2(50)

340

= 0.29 s

11



2.

If an echo is heard one second after the holler and reflects off canyon walls which are a distance of 170 meters away, then what is the speed of the wave? Answer: 2s = v x t v=

2s t

=

2(170) 1

= 340 m s-1

6.3 ANALYSING REFRACTION OF WAVES change of direction of the propagation of waves 1. The refraction of water waves occur when there is a ……………………………………… traveling from a medium to another medium due to a change of speed.

Figure 6.30 2.

frequencyy frequenc After refraction, the wave has the same …………………………. but a different speed, wavelength and direction. ………………………….

12



Refraction of Water Waves

λ1

Deep

λ2

shallow Figure 6.31

towards 1. When the water wave travel from a deep area, the direction of the waves is refracted ……… (towards/away from) the normal. greater (greater / smaller) than the angle of 2. The angle of incidence, i of the water is ………. refraction, r 3. When the refraction of a wave happened , the frequency, f does not change but the wave wa vele len n th , λ , .................................................................. the s eed and the direction direction o ro a ation..............of the wave change. ……………… Exercise 6.3 1. Complete the table below to show the properties of refracted water waves when wave travels from one area to another area of a different depth. Use the words given.

Decreases

Increases

Bends towards the normal

Properties of refracted water waves Wavelength Velocity Frequency Direction of travel

Unchanged

Bends away from the normal

Deep water to shallow water Decreases Decreases Decreases Decrea ses Unchanged Bends towards towards the normal normal

13

Shallow water to deep water Increases Increases Increases Increa ses Unchanged Bends away away from the normal



2. On each of the following diagram, draw the refracted wave by the perspex. (a) (b)

(c)

(d)

(e)

(f)

•

3.

-1

A plane wave has a wavelength of 2 cm and a velocity of 8 cms as it moves over the surface of shallow water. When the plane wave moves into an area of greater, depth, its -1 velocity becomes 12 cms . What is the a. wavelength b. frequency of the wave in the area of greater depth? •Answer: 8 2 (a) λ1 = 2 v1 = 2 v = f λ = 12 λ2 λ2 =

(b)

f=

v λ

v1

v2 = 12

?

=

12 3

v2

= 4 Hz

14

=

λ1 λ2

λ2 =

12 x2 8

= 3 cm



Refraction of water wave of the sea water

Figure 6.32 1.

Why are the speed and wavelength of waves in the middle of the sea almost uniform? The depth of water in the middle of the sea is almost uniform. ………………………………………………………………………………………

2. What do you think would happen to the wave speed if the depth of water water is increased? The speed increases ………………………….. . 3. Why do the distances between the wave fronts decrease as the waves approach the beach? On approaching the beach, the depth of water decreases. The speed of waves …………………………………………………………………………………………… decreas decr easee and the wavelen wavelen th is decrea decreased. sed.

4.

Why is the water in the bay stationary compared to the water at the cape? The depth of water varies across the area of the bay …………………………………………………………………………………………… The energy of the water wave spreads to a wider area as compared to the region near the cape The amplitude of the water wave near the bay is low and hence the water at the bay is comparatively still

15



Refraction of Light Waves

normal

air glass block

Figure 6.33 1. When a ray propagates from one medium to an optically denser medium, the ray refracts towards …………………(towards / away from) the normal. decreases 2. The speed of light …………….(decreases/increases) as it propagates in the glass block, causing it to alter the direction of propagation. Refraction of Sound Waves

Figure 6.34 (a)

Figure 6.34 (b)

cold 1. Sound waves travel faster in warm air than in …….. (cold/hot) air.

2. On a hot day, the hot surface of the Earth causes the layer of air near the surface to be warmer (warmer/cooler) ………… refracted (reflected/refracted) away from the Earth. 3. This causes sound waves to be …………. slower slower/faster )in the cooler layer of air 4. On a cool night, the sound waves travel ………….( near the surface of the Earth than in the upper, warmer air. The waves are refracted towards the Earth. night Hence, sound can be heard over a longer distance on a cold ……….(night/day) compared with a hot day .

16



6.4 ANALYSING DIFFRACTION OF WAVES the spreading out of waves when 1. Diffraction Diffraction of waves is …….......................................................................... they move through a gap or around an obstacle.

2. The effect of diffraction is obvious only if small (a) the size of the aperture or obstacle is …………..small / large enough. large (b) the wavelength is ……………… small /large enough. 3. 4.

speed Frequency, wavelength and …………………of waves do not change dire di rect ctio ion n o ro a at atio ion n an and d th thee at atte tern rn of the waves are change The …………………………… …………………………………………. …………….

Diffraction of water waves

Exercise 6.4 1. The table shows the properties of diffracted water waves as they pass through a gap. Choose the correct answers given into the blanks.

Unchanged

Increased

Decreased

Properties of diffracted water waves Wavelength Speed Frequency

17

After passing through a gap Unchanged Unchanged Unchanged



2. Complete the diagrams below by drawing the wave fronts to show the diffraction of water waves. (a) Narrow gap ≤ λ

(c)Wider obstacle

(b) Wider gap > λ

(d) Narrow obstacle

From the diagram above, narrower 1. The ………….(narrower/wider) the gap, the more the waves spread out. little 2. When the gap is much wider than the wavelength of the waves, there is …………. (little/more) diffraction.

18



Diffraction of light waves

Figure 6.40 Diffraction of light through a single slit Smaller bright strip at the centre

Larger bright strip at the centre

Figure 6.41 (a) Wide slit

Figure 6.1(b) Narrow slit

1.

The diffraction of light waves occur when the light waves pass through a small slit or small pin hole. 2. The wider middle bright fringe shows that the light waves diffracted after pass through a narrow slit. less 3. If the slit becomes wider, diffraction pattern becomes ………….. (less/more) distinct.

Diffraction of sound waves

Figure 6.42

19



1. A listener is requested to stand on the other side of the corner of the wall so that the radio is beyond his vision. 2. The listener is able to hear the sound of the radio although it is behind the wall. 3. It is because the sound of the radio spreads around the corner of the wall due to diffraction of sound. 6.5 ANALYSING INTERFERENCE WAVE

1. Interference is the superposition of two waves from two coherent sources meet amplitude frequency frequen cy 2. Two waves are in coherent if they are of the same ………………….and ………………,

3. There are two types of interference : (a) Constructive interference (b) Destructive interference Principle of superposition When two waves overlap, the resultant displacement is 1. The principle of superposition superpositio n states that……………………… that……………………………………………………… ……………………………… equal to the sum of the displacements of the individual wave ………………………………………………………………………………………………… the crests or troughs of both waves coincide to produce 2. Constructive interference occurs when………………………………………………… a wave with maximum amplitude.

3.

the crests of one wave coincide with the trough of Destructive interference occurs when………………………… when……………………………………………………… …………………………… the other waves to produce a wave with zero amplitude amplitude

4. (a)

Constructive Interference

+

=

Before superposition

During superposition

Figure 6.50 (a)

+

=


During superposition superpositi on

Figure 6.50 (b)

20



When the vertical displacement of two waves are in the same direction as in Figure 6.50 constructive (a) and (b), …………………………(constructive/destructive) interference occurs. (b)

Destructive Interference

+

=



Figure 6.51 If a wave with a positive displacement meets another with a negative displacement of the same magnitude, they cancel each other and the combined amplitude becomes zero. ………. Interference of Water Waves

Figure 6.52: Interference of water waves 1.

At the points of constructive interference, the water moves up and down with a large …………(large/ small) amplitude

2.

antinodes nodes/antinodes) The points of constructive interferences, is known as …………..( nodes The points of destructive interferences is known as ………………(nodes/ant ………………(nodes/antinodes). inodes).

21



Exercise 6.5 B C A

Figure 6.53 1.

Figure 6.53 shows the interference pattern of water by two coherent sources of water waves. constructive interference. (i) At point A, two crest meet resulting in ……………………….. constructive (ii) At point B, two through meet resulting in ……………………..interference. destructive (iii) At point C, a crest meet a trough resulting in …………………interference. 2.. Complete the table below. Before superposition


22

After superposition


3.


Categorize each labelled position as being a position where either constructive or destructive interference occurs.

A,B

(a) Constructive interference:……………………. C,D, E, F (b) Destructive interference:…………………….. interference:…… ……………….. .

4.

The diagram shows a full-scale interference pattern of a ripple tank experiment 2 seconds after vibration started. The crests of the water ripples are represented by the dark lines. (a) What is represented at P at this instant? P is between two crest. Therefore, P represents a trough …………………………………………………………. (b) What is the frequency of the vibrator? The diagram shows crests from each source. In 2 seconds, 4 crests are produced. ………………………………………………………… 4 Thus the frequency is = 2 Hz 2

5.

Two dot vibrators which has a separation of 5.0 cm are placed on a water surface in a ripple tank. The distance between two adjacent antinodes on a screen is 3.0 cm. If the perpendicular distance between the dot vibrators and the screen is 10.0 cm, what is the wavelength of the water waves? Answer: 5.0 x3.0 λ= 10.0

= 1.5 cm

23



Complete the crossword puzzle.

1.

coherent Two sources are said to be ……………………if they have the same frequency of vibration and a zero or constant phase difference.

2.

interference We can use a ripple tank to observe …………………..patterns of water waves.

3.

constructive ..interference occurs. Antinodes are points where ………………

4.

destructive Nodes are points where ………………interference occurs.

5.

antinode Antinodal lines are lines joining ………………………

6.

nodes Nodal lines are lines joining …………………………

24



Interference of Light Waves

A ray of light passes through the single slit and reaches the double-slit will give rise to two coherent light rays.

1. Interference occur when at least two coherent light waves overlap or superpose 2. The superposition of 2 rays produces: constructive interference (i) ……………………………………… destructive interference. (ii)……………………………………… 3.

bright (bright/dark) fringe When constructive occurs there will be a ………… dark When destructive occurs there will be a …………(bright/dark) fringe

25


4.


The wavelength of monochromatic light can be found by the formula:

is the distance between the slits a = ……………………………… ………………………………………………….. ………………….. is the distance between consecutive bright or dark fringes x = …………………………………………………. is the distance between the double-slit and the screen D = ………………………………………………….

Exercise 6.51

1. In a Young’s double slit experiment, a light of wavelength 633 nm passes through Vertical fringes are observed on a screen placed 4 m from the slits. (i) Calculate the distance between two adjacent bright fringes. (ii) What will happen to the distance between two adjacent bright fringes if a light of shorter wavelength is used? Answer: (a) λ = 633 nm = 633 x 10-9 a = 0.5 mm = 0.5 x 10-3 m D = 4 m x =

− 633 x10 9 x 4

0.5 x10

−3

x = 5.064 x 10-3 mm

(b)

If λ is smaller, x will also be smaller. Therefore , the distance between two adjacent bright fringes of light will smaller.

14 mm

26



2. The wavelength of light can be determined with a double-slit plate. The diagram above shows the pattern of interference fringes obtained in a Young’s double-slit experiment. The separation distance of the two slit is 0.20 mm and the distance between the screen and the double-slit plate is 4.0 m. Calculate the wavelength of the light used in the experiment. -4

Answer: 7x = 14 mm -3 x = 2 mm = 2 x 10 m

a = 0.2 mm = 2 x 10 m − − 2 x10 x2 x10

4

λ =

D = 3.0 m

3

4

= 1 x 10-7 m Interference of Sound Waves

The wavelength of sound wave can be found by the formula:

distance between two loudspeakers a = ……………………………… ………………………………………………….. ………………….. distance between two consecutive loud places x = …………………………………………………. perpendicular perpend icular distance distance between between 2 speakers speakers D = …………………………………………………. Exercise 6.52

1. Two loud speakers placed 2 m apart are connected to an audio signal generator that is adjusted to produce sound waves of frequency 550 Hz. The detection of loud and soft sounds as a person moves along a line is at 4.0 m from the loudspeakers. Calculate the (a) wavelength (b) speed of the sound waves.

27



Answer: (a) a = 2 m D = 4.0 m 2 x1.2 λ= = 0.6 m 4.0 (b) f = 550 Hz Hz V = f λ = 550 x 0.6 -1 = 330 m s 6.6 Analysing Sound Waves

1. Sound waves are longitudinal waves which require a medium for its propagation. amplitude 2. The loudness of the sound is depend to the …………………

frequency frequen cy 3. The pitch of the sound is depend to the ……………………... …………………….. .

28


4.


a phenomenon when a sound wave has been reflected off a Echo is …………………………………… …………………………………………………………………… ……………………………… surface , and is heard after the original sound.

Application of Sound Waves 1. Ultrasonic waves with frequencies above 20 kHz cannot be heard by human ear. 2. The ultrasonic ruler is used to measure the distance between itself and a target. 3. The depth of sea water can be calculated using the formula :

2d = v x Exercise 6.60

29



boundar When a wave reaches the (1) .......... ...... .... from one medium to another medium, a portion of the wave undergoes reflection while the other portion of the wave undergoes transmission across the boundary. loudest sound will The (2)………. will be heard when the angle of incidence , i equals the angle of reflection, r re le lecti ction on Therefore, we can say that sound waves obey the laws of (3)……….. Echoes that are causes by multiple reflections from numerous reflecting (4)…….. surfaces of a large hall can create an impression that sound lasts for a long time.

If the reflector is near to the sound source, the reflected sound will overlap the origin sound. It will not be heard as a separate sound, but as a prolonged origin reverberation sound known as (5)…………

2.

In an expedition to determine the depth of a freshwater lake using an ultrasonic ruler, a pulse of ultrasonic sound is generated and travels to the bottom of the lake and reflected by it. The time taken by the pulse to travel to the bottom of the lake and return to the ruler is 0.35 s. If the speed of sound in freshwater is 1482 m s-1, calculate the depth of the lake. Answer: v = 1482 m s-1, t = 0.35 s 2 d = v x t 1482 x0.35 d= = 259.35 m 2

3.

. Fill in the blank. Field Medicine

Industry

Application Sound waves of high energy are directed to the kidney stones to destroy them in the cavity of the kidney. Sound waves of high energy are directed to the kidney stones to destroy them in the cavity of the kidney.

30



6.7 Analysing Electromagnetic Waves

1. The electric and magnetic field vibrate ………………..(perpendicular/parallel) to perpendicular perpend icular each other and to the direction of propagation. 2. Properties of electromagnetic waves (i) Transverse waves (ii) Do not require require a medium medium to propagate propagate and can travel travel in a vacuum vacuum 8 -1 (iii) The waves travel at the speed of light, c = 3 x 10 ms (iv) Undergo the same waves phenomenon : reflection, refraction, diffraction and interference. 3. Sources and applications of electromagnetic waves in daily life Type of em wave

Source

Application

(a) telecommunications (b) broadcasting : tv and radio transmission Oscillating electrical (a) satellite transmissions Microwave charge in a microwave (b) radar -3 -1 λ = 10 – 10 m transmitter (c) cooking (a) night vision Infrared Hot bodies, bodies, the sun and and (b) thermal imaging and physiotherapy -6 -3 λ = 10 – 10 m fires (c) remote controls (a) sight Visible light -7 The sun, hot objects, light (b) (b) photosyn photosynthesis thesis in plants plants λ = 10 m bulbs, fluorescent tubes (c) photogra photography phy Ultraviolet (a) identification of counterfeit notes Very hot objects, the sun, (b) (b) productio production n of vitamin-D vitamin-D radiation -9 -7 (c) Sterilisation to destroy germs λ = 10 – 10 m mercury vapour lamps (a) Radiothe (a) Radiotherapy rapy X-ray -11 -9 x-ray tubes tubes (b) Detectio (b) Detection n of cracks cracks in building λ = 10 – 10 structures m (a) Cancer treatment Gamma rays Radioactive Radioac tive subtances subtances (b) Sterilisation of equipment -14 -10 λ = 10 – 10 (c) Pest control in agriculture m

Radio waves -1 5 λ = 10 - 10 m

Electrical oscillating Electrical oscillating circuit

31



Exercise 6.70

1. The diagram below shows the pattern of spectrum electromagnetic. In the boxes provided, write the names of the parts given .

Radio wave

microwave gamma ray

x-ray visible ray infra-red ray ultraviolet

wavelength

Gamma ray

X-ray

Ultra Violet

Visible light

infrared

microwave

frequency

2.

Table 6.70 shows electromagnetic waves P, Q, R and S and their uses Electromagnetic waves P Q R S

Uses Remote control Radar system Photograph Kill cancerous cells

Table 6.70 Identify P, Q, R and S Answer: P = Infra-red rays Q = Microwaves R = Visible light light S = Gamma rays

32

radio wave



Reinforcement Chapter 6 Part A : Objective Questions

1. Calculate the frequency of the given wave above A. B. C. D. E.

8 Hz. 1/8 Hz 4 Hz. ¼ Hz 12 Hz

2. Which of the following is NOT an electromagnetic wave? A. B. C. D.

x-ray. Gamma ray water wave microwave.

3. Which of the following cannot travel through vacuum? A. B. C. D.

4.

x-ray gamma ray sound wave light wave.

Based on the given diagram above calculate the wavelength. A. B. C. D. E.

4 cm 8 cm 10 cm 15 cm 20 cm

33



5. Wave length of given wave does NOT depend on. A. B. C. D.

6.

velocity. Frequency Amplitude Period.

What is the phenomenon shown above? A. reflection. B. Refractio Refraction. n. C. Interference. 7.

5

-1

A given wave wave travels at a speed of 4 x 10 ms . If the frequency of the wave is 1000 Hz, calculate the wavelength A. B. C. D. E.

100 m 200 m 300 m 400 m 500 m

8. Which of the following is a common characteristic of visible light, ultraviolet rays, infrared rays, gamma rays and X-rays? A. B. C. D.

Influenced by magnetic field. Possess the same frequency. Possess the same wavelength. Possess the same velocity in vacuum.

9. Which of the following electromagnetic waves are arranged in the order of increasing wavelength. A. B. C. 10.

Visible light, X-rays. Radio waves. Infrared waves. X-rays. Visible light. Infrared waves .Radio waves. Radio waves, X-rays. Visible light. Infrared waves.

Which of the following waves cannot travel through vacuum? A. Sound waves B. X-rays C. Radio waves

34



Part B: Structured Questions

Figure 1 1. Figure 1 shows the use of sonar equipment to measure the depth of the sea. (a) State the phenomenon of sound wave applied in sonar equipment. equipment. Reflection Reflectio n ………………. [1 mark] 5 (b) Sound waves with frequency of 6.0 x 10 Hz are used to determine the depth of -1 the sea. [speed of sound in sea water = 1500 m s ] (i)

(ii)

What is the wavelength of the sound wave in sea water? v 1500 λ= = = 2.5 x 10-3 m 5 f 6.0 x10 [2 marks] If the time interval between the instant the sound wave is sent to the instant the echo is received is 1.5 s, what is the depth of the sea d=

vt

2

=

1500 x1.5 2

= 1125 m

[2 marks]

2.

Figure 2 A ping pong ball is held with a string and placed near a loudspeaker as shown in Figure 2 The loudspeaker emits a low frequency sound and the ping-pong ball seems to vibrate to it.

35



(a) Explain how the sound from the loudspeaker produces vibration on the ping pong ball. The vibration of the loudspeaker moves the air molecules around it. The sound wave produced by the loudspeaker transfers energy to the ping pong ball and and causes causes it to move (b) What will happen to the vibration of the ping pong ball if the loudness emits (i) a louder sound? The ping pong ball vibrates with greater amplitude (ii) a sound with a higher pitch? The ping pong ball vibrates with higher frequency.

3.

(c) If the frequency of the sound is 50 Hz, calculate the wavelength of the sound -1 produced. [Assume the speed of the sound in air in 350 ms ] v 350 = = 7m λ= 50 f (a) Figure 3 shows two sets of ripple tanks used to study diffraction of waves.

(i)

Figure 3.1 Figure 3.2 What is meant by the diffraction of waves. Diffraction Diffractio n is the spreading spreading out out of waves when when they move through through a gap or around an obstacle

(ii)

Which of the two sets will show a bigger effect of diffraction. Explain your answer. The set shown in Figure 4.1 will show a bigger effect of diffraction. This is because the narrower the gap, the more the waves spread out.

(iii)

Redraw and complete Figure 3.1 and Figure 3.2 to show the differences between the two diffraction patterns.

(iv)

State the characteristic to the diffracted waves in terms of waves in terms of wavelength, frequency, speed and amplitude compared to the incident waves. (a) Wavelength remains unchanged (b) Frequency remains unchanged (c) Speed remains unchanged (d) Amplitude become becomess smaller compared compared to the incident incident waves

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4. You are assigned to investigate the properties of waves that could be used in broadcasting and communication. Table below shows the properties of six types of waves P, Q, R, S T and U. Wave Type of wave P Q R S T U

Transverse Transverse Transverse Transverse Longitudinal Longitudinal

Material medium for propagation Not required Not required Not required Not required Required Required

Speed of wave 8

-1

3 x 10 ms 8 -1 3 x 10 ms 8 -1 3 x 10 ms 8 -1 3 x 10 ms -1 330 ms -1 10 ms

Penetrating power Penetrates matter Absorbed by glass Refracted by glass Medium Weak Weak

Based on the table, select the most suitable wave that could be used in broadcasting and communication and give your reasons. [10 marks] Answer: Characteristics It is transverse transverse wave wave It does not not require material medium for propagation propaga tion It travels at a very high high speed It does not not need a high high penetrating penetra ting power

Reason It can be modulated modulated by the signal signal frequency frequency It can travel travel through vacuum

Information can be sent Information sent immediately immediately to any any destination Information Informatio n can be transmitted transmitted in a straight straight line from one place to another

Wave R is chosen because of it is transverse wave, not require material medium, very high speed and doesn’t need a high penetrating power.

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5. Figure 5.1 shows the arrangement of the apparatus for an experiment to study a wave phenomenon.

Figure 5.1 Figure 5.1 shows the bright and dark bands of the wave pattern formed on the white piece of paper produced by the vibration of two spherical dippers on the water surface.

Figure 1.2 Figure 5.2

Figure 1.3 Figure 5.3

(ii) Observe Figures 5.2 and 5.3. Compare the wave patterns produced by the spherical dippers. State the relationship between the distances of the two coherent consecutive node or antinodes lines. [5 marks] Answer: i. The spherical dippers are closer in Figures 5.2 and they are futher apart in Figure 5.3 ii. The wavelength is the same in Figure 5.2 and 5.3. iii. The distance of two separation between two consecutive antinodes or node lines is smaller in Figure 5.3 than 5.2 iv. The angle between the successive antinodes or node lines is smaller in Figure 5.3 than5.2 v. The smaller the distance between two coherent sources, the larger is the distance between the two consecutive antinodes or node lines.

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Part C: Essay

1.

Figure 6.0 shows the arrangement of the apparatus for an experiment to study a wave phenomenon.

Figure 6.0 Figure 6.1 shows the bright and dark bands of the wave’s pattern formed on the white paper when plane waves passes through the narrow and wide gaps.

Narrow gap Figure 6.1(a) (a)

Wide gap Figure 6.1(b)

Name the wave phenomenon shown in figure 6.2. Diffraction

(b) (i)

[1 mark]

Explain how the dark and light bands are formed on the white paper. [4 marks]

√ Figure / Troughs act as a concave lens

√ Figure / Crests act as a convex lens

√ Figure / Every troughs will diverge the light, dark fringes are formed B

D

√ Figure / Every crests will B

D

B

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D

B

converge the light, bright fringes are are formed



(ii) Observe Figure 6.2(a) and (b). Compare the wave’s patterns and the wavelength of the waves before and after they pass through the gaps. Relate the size of the gaps, the waves patterns and the wavelengths to deduce a relevant physics concept. [5 marks] a. In figure 6.1(a), 6.1(a), size of the waveleng wavelength th is the same as size of the the gap // In figure figure 6.1(b), size of the gap is wider than size of the wavelength b. In figure 6.1(a) 6.1(a) and figure figure 6.1(b), 6.1(b), size of the wavelength wavelengthss are the same same before and after they pass through the gaps. c. The waves emerging from the narrow gap in figure 6.1(a) is circular wave fronts d. The waves emerging from the wider gap is plane wave fronts e. When a wave passes through a gap, the wave spreads. The narrower the gap the greater the spreading of the wave

(c)

Figure 6.3 shows the seashore of a fishing village. During the rainy season, waves are big. One year the waves eroded the seashore, caused the jetty to collapse and damaged the fishermen’s boats.

Figure 6.3 To prevent similar damage in the future, the fishermen suggest building retaining walls and relocating the jetty. Make further suggestion of ways to help the fishermen solve their problems. You should use your knowledge of reflection, refraction and diffraction of waves to explain these suggestions, to include the following aspects. (i) the design and structure of the retaining wall, (ii) the location of the new jetty (iii) the size or energy of the waves [10 marks] Answer: 1. Build slanting slanting barrier barrier to reduce reduce speed of wave 2. Build the rough rough barrier barrier to reduce reduce reflection reflection of the waves waves 3. Build the new new jetty at the the bay because because the water water is calm at the bay 4. Build the small small opening opening surround surround the bay because diffraction diffraction happens happens at the the opening opening 5. Build the barrier barrier at the the bay because because the wave wave is spread spread according according to the shape shape of the bay

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Chapter 6 Waves Teacher's Guide 2009

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