. Physics Module Form 5
1.1
chapter 1 : Waves
GCKL 2011
U N D E R S T A N D I N G
W A V E S
What is meant by a wavefront
An imaginary line that joins all the points on the crest of a wave.
State the direction of propagation of waves in relation to wavefronts
The direction of propagation of a wave is perpendicular to its wavefront.
What is transverse wave?
A transverse wave is a wave in which particles of the medium medium oscillate in the direction of the propagation of the waves. Water waves and electromagnetic waves are examples of this type of waves. A longitudinal wave is a wave which the particles of the medium
What is longitudinal wave?
oscillate in the direction parallel to the direction in which the wave moves Sound waves is the example of this type of waves.
F il l i n the blank wi th th e corr corr ect answe answerr given given below below
frequency
period
Hertz ( Hz)
amplitude amplitud e
amplitude of an oscillation is the maximum displacement 1. The displacement for one complete oscillation .
2. The
period
of the oscillation is the time taken to complete one oscillation.
3. The frequency of the oscillation is the number of complete oscillation made in one second. The SI unit is Hertz ( Hz) L abel abel th e graph below below and fi ll in the blank blank with corr corr ect answe answerr .
Displacement – Displacement – time time graph
4. In the displacem di splacement ent – time time graph as shown above, amplitude is r epresented epresented by the symbol a T of and period is represented by the symbol of
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Displacement – Displacement – distance distance graph
5. In the displacem di splacement ent – distance distance graph as shown above, amplitude is represented by the symbol of a λ and wavelength is represented by the symbol of loses 6. Damping is occur when in an oscillating system when the system ( gain / heat loses) energy to surrounding in the form of ( heat / chemical chemical ) energy.
7. The force responsible for damping is called dissipative ( equilibrium / dissipative)
forces.
8. In a simple pendulum, its natural frequency depending on its mass ).
( length /
length
9. When an oscillating systems driven at its natural frequency, frequency, the system is said to be at reasonance ( damping / reasonance) reasonance)
10. A wave travels with a speed of 3.0 x 10 8 ms-1 (a) What is the frequency frequency of the wave if its wave length is 1.0 m? (b) Another wave is travelling with the same speed speed but has a frequency frequency of 1.5 x 1012 Hz. What is the wavelength of the wave? Solution.
Wave speed , v = f λ 8
(a) f = 3.0 x 10
(b) λ = v / f 8
= 3.0 x 10 1.5 x 1012
1.0
8 = 3.0 x 10 Hz
= 2.0 x 10 -4 m
1-2
. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
11. The displacement – time graphs and displacement – distance graph describe the motion of a particular wave. Determine the speed of the wave. a) Displacement – time graph (b) Displacement – distance graph S/cm
S/c
t/s 2
4
6
2
4
solution : v = f λ,
f=1/T
from (a) : T = 4 s, f = 0.25 Hz
from (b) : λ = 4 cm
v = f λ
= 0.25 x 4 -1 = 1 cm s
12. Displacement/cm
5 -5
3
1
2 Distance/cm
Based in the displacement-distance graph of a wave, find (a) the amplitude (b) the wavelength of the wave ( ans : 5 cm) ( ans : 2 cm)
13. Calculate the frequency of the given wave below
f = 1/T = 1/4 = 0.25 Hz.
1-3
6
l/cm
. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Practise 1.1
1.
4. The period of oscillations of a simple pendulum increases when the ________________________ increases. A length of the pendulum B mass of the bob of the pendulum C acceleration due to gravity
Diagram 1.11 Base on the diagram 1.11 above, which distance represents the amplitude?
5. Diagram 1.14 shows a wavefront pattern produces by a dipper vibrating at a frequency of 12 Hz in a ripple tank.
2. Diagram 1.12 shows how displacement how varies with time.
Diagram 1.12
Diagram 1.14 What is the speed of the waves? -1 A. 2 cms-1 B. 8 cms -1 -1 C. 12 cms D. 18 cms -1 E. 36 cms
Which of the following is true? Amplitude/ m
A 0 .1 B 0.2 C 0.1 D 0.2
Period / s
0.50 0.50 0.25 0.50
Frequency / Hz
2 1 4 2
9. Diagram 1.15 shows the cross section of water waves.
3. Diagram 1.13 shows the displacementtime graph of an oscillating system
Diagram 1.15 Which of the following statements is true about the water waves? A. T and U have the same phase B. Wave energy is transferred from position S to U. C. The wave length is the distance between S and U D. The particles at U oscillates in a direction parallel to the direction of the wave propagation
Diagram 1.13 The system which produces this graph is having A. a perpertual oscillation B. a forced oscillation C. a damped oscillation D. a resonance
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011 11. Diagram 1.16 shows the displacement distance graph. The frequency of the wave is 5.0 Hz.
10. The graphs show the cross-sections of
water waves. Which wave has the greatest energy?
What is the velocity of the wave? A. 50 cms-1 C. 100 cms-1 B. 75 cms-1 D. 150 cms-1 11. Diagram 1.16 shows a silky spring being moved left and right continuously.
11. Which graph represents a wave with
Diagram 1.16
amplitude of 4.0 cm and period of 0.05 s (a)
Complete the sentence below by ticking
(√) the correct box. The wave produced by the slinky spring is a Transverse wave Longitudinal wave
√
b). On diagram 1.16. mark ‘ X’ on any of the crest of the wave.
c) Complete the following sentence by underlining the correct phase in the bracket.
d) What is transferred by the wave? Energy
1-5
. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
ANALYSING REFLECTION OF WAVES .
1.2 1.2
1. complete the diagram 1.21 below to show the reflected waves.
Diagram 1.21 2. Fill in the box with the correct answer.
Incidence ray
i = inci dence angl e r = r eflected angl e
Reflected ray
3. Draw the correct pattern of reflected water waves. wavefronts (a) reflector
wavefronts (b) reflector
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
(c) Reflected light ray Incident light ray
(c) Compare the following quantities before and after reflection. (i)
velocity: ____remain the same__________
(ii)
frequency:_ ____remain the same__________
(iii)
wavelength: ____remain the same__________
(iv)
direction:_____ changes after undergoing reflection.
d)
In reflection , the angle of reflection is always equal to angle of reflection
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Practice 1.2
1. Which of the following characteristic of waves changes when the wave are reflected? A. Direction of propagation B. Wavelength C. Frequency D. Speed 2. What happens to the wave length and the magnitude of the velocity of water waves when it is reflected? Wavelength A. Unchanged B. Increases C. Decreases D. Increases
Magnitude of velocity Unchanged Decreases Increases unchanged
3. Diagram 1.22 shows a sound wave reflected from a concrete wall.
Diagram 1.22 Which statement is correct about the reflected and incident waves? A. The speed of the reflected waves is the same as the speed of the incident waves. B. The wavelength of the reflected waves is shorter than that of the incident waves. C. The frequency of the reflected waves is lower than that of the incident waves. D. The directions of the reflected waves are always at right angles to the incident waves. 4. Echo is a phenomenon caused by A the refraction of sound waves B the reflection of sound waves C the diffraction of sound waves D the polarization of sound waves 5
Diagram 1.23 shows the wavefront of a plane wave wave incident on a plane reflector. Which comparison is correct about the reflected sound wave and the incident sound wave?
Diagram 1.23 A. B. C. D.
The wavelength of the incident wave is shorter than the reflected wave. The speed of the incident wave and the reflected wave is the same. The frequency of the incident wave is less than the reflected wave. The angle of incident wave is greater than the angle of reflection of the reflected wave. 1-8
. Physics Module Form 5 6.
chapter 1 : Waves
GCKL 2011
Diagram 1.24 show the apparatus is used to investigate the reflection of sound waves. At what position of the cardboard tube is adjusted until a loud ticking sound of the stop watch is heard?
Diagram 1.24 7.
Diagram 1.25 and Diagram 1.26 show the water and sound waves propagating towards a reflector. Incident
i r
Reflect edwave
Norm Direction of reflected
Diagram 1.25
Card board
Stop watch
E
Diagram 1.26 ii) With reference to Diagram 1.25 and Diagram 1.26 , compare the incident and reflected angle, wavelength, frequency, speed and direction of propagation of the reflected Incident angle in diagram 1.25 and 1.26 is equal to reflected angle, the wavelength in diagram 1.25 and diagram 1.26 remain the same, frequency of diagram 1.25 and 1.26 remain the same, speed of diagram 1.25 and 1.26 remain the same and direction of propagation of direction of propagation of diagram 1.25 and diagram 1.26 is changing.
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. Physics Module Form 5
1.
Waves can be refracted as they move from one medium) to another.
2.
When water waves travel from one area to another area of different depth, their speed changes ( remain / changes ) and the frequency remain (remain / changes) .
3.
The wavelength of waves in deep area is the shallow area.
4.
When waves travel from a denser medium to less dense medium , they refracted towards (away / towards) to normal.
5.
Draw a diagram to show refraction of wave
GCKL 2011
Analysing refraction of waves.
1.3 Describe refraction of waves in terms of the angle of incidence, angle of refraction, wavelength, frequency, speed and direction of propagation
chapter 1 : Waves
medium
( volume /
longer ( shorter / longer ) than that in
Diagram 1.30 Diagram 1.30 shows the incident ray is refracted ... towards ( away / towards ) to normal.
Complete the diagrams below.
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Why is the wave bend according to the shape of the shoreline when they are approaching the beach?
Diagram 1.31: the shape of shoreline when they are approaching the beach uniform speed reduce towards
depth of the sea refraction
parallel refracted
shallower wavefront
In the centre of the ocean, the water wave travel at uniform speed as the depth of the sea water is uniform. Hence the wavefront are straight and parallel to each other. When the waves reach the coast, the water is shallower . Wave speed is reduce and refraction occurs. The wavefront are refracted and become closer to each other. Refraction causes the wavefront to be bent towards the normal and this results the wavefront following the shape of the coastline.
Figure 1.32
Figure 1.33
Why sound can be heard over a longer distance on a cold night compared with a hot day as illustrated in diagram 1.32 and 1.33
Sound wave travel faster in warm air ( warm air / cool air) than in cool air ( warm air / cool air). On hot day, the hot surface of the earth causes layer of air ( layer of air/ layer of density) near the surface to be warmer ( colder / warmer). This causes sound waves ( light waves / sound waves) to be refracted away ( away / closer) from the earth. During night time, the sound waves travel slower ( slower / faster ) in the cooler layer of air near ( near / upper ) the surface of the earth than in the upper ( near / upper ) warmer air. As a result , the wave are refracted (refracted / reflected) towards the earth. This explain why sound can be heard over a longer distance on a cold night compared with a hot day.
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Practice 1.3
1. Diagram 1.34 shows water waves propagating through a Perspex block in a ripple tank.
3. When water waves pass from deep water into shallow water, how do the speed, wavelength and frequency change?
A B C D
Diagram 1.4 Which wave pattern is observed when the waves pass through the perspex bloc.
Speed Increases Decreases Increases Decreases
Wavelength Decreases Increases Increases Decreases
Frequency No change Decreases No change No change
4. An observer cannot see the coin in an empty glass as shown in figure (a). However he can see the coin when the glass is filled with water as shown in figure (b) Figure (a)
Figure (b)
The observer can see the coin in Figure (b) due to
2. Diagram 1.35 shows water waves propagating in an area of different depths.
A B C D
the total internal reflection of light the refraction of light the reflection of light the diffraction of light
4. A tilted basin contains water. Water is dripped at a constant rate into the basin as shown in the diagram below. Diagram 1.35 Which of the following diagrams shows the propagation of the waves correctly?
Which pattern of the wavefronts will be observed in the basin?
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. Physics Module Form 5
chapter 1 : Waves
5. A ray of light passes from water to air. Which labeled arrow shows the direction of the ray in air?
GCKL 2011 Wavelength of the waves in region X is longer than region Y.
(iii) Relate the depth of water to the wave length of the waves. The deeper the water, the longer the wavelength.
(iv) Name the wave phenomenon involved. Refraction.
c) Explain why the wave front of the sea will follow the shape of the shore when it approaches the shore. 6. Diagram 1.36 shows the side view of two ripple tanks. When the motors are switched on, water waves with the same frequency are produced,
Diagram 1.36
In the ocean, wavefronts are straight and parallel as the wave speed is uniform. When a wave moves towards the shore, the depth of the sea water decreases, the velocity of the water decreases. Refraction occur and the sea water refracted towards the normal. This causes the wavefront follow the shape of the shore. 7. Diagram 1.38 (a) shows the wave formed without a flat piece of plastic and diagram 1.38 (b) shoes the wave with a flat piece of plastic.
Diagram 1.37 shows the waves formed on the screens.
Diagram 1.38(a)
Diagram 1.38(b)
a) Observe the diagram and state the difference between diagram (a) and diagram (b). The wavelength of diagram1.38 (a) is uniform while wavelength in diagram 1.38(b) is shorter when passes through the plastic .
Diagram 1.37 a) What is the meaning of frequency? Number of complete oscillations in one second b) Observe diagram 1.36 and diagram 1.37.
b)
Using your answer, state the relationship between depth and wavelength The deeper the .water, the longer the wavelength c) Name the wave phenomenon involve Refraction .
(i) compare the depths of the water in region X and region Y. The depth of region X is greater than in region Y.
(ii) Compare the wavelength of the waves in region X and region Y.
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. Physics Module Form 5
1.4 Describe diffraction of waves in terms of wavelength, frequency, speed, direction of propagation and shape of waves
chapter 1 : Waves
GCKL 2011
ANALYSING DIFFRACTION OF WAVES.
1. Diffraction is the spreading out of waves when they move through a gap or around an obstacle. 2. The narrower
the gap, the more the wave spread out.
3. When the width of the gap is approximately the size of the wave length of the waves, the diffracted waves spread out more. 4. When the gap is much wider than the wavelength of the wave, the diffraction is little.
5. After diffraction, the frequency remain unchange, the wavelength remain unchange, and the speed remain unchange, 6. The direction of propagation of the diffracted waves changes. Draw a diagram to show diffraction of waves
Complete the diagrams below.
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Practice 1.4
1. Which of the following figure is true to show the diffraction of a water wave?
3. Diagram 1.42 shows waves moving towards a harbour.
2. Diagram 1.40 shows the bright and dark bands of the wave patterns formed on the screen when plane waves pass through narrow and wide gaps.
Diagram 1.42 a) (i) What is the meaning of diffraction? The spreading or bending of waves around an obstacle or small opening. (ii) Draw the wave pattern of the waves after passing through the entrance of the harbour.
Diagram 1.40 a) Observe Figure 1.40 compare the waves pattern and the wavelength of the waves after they pass through the gaps. b) The entrance is made wider to allow more ships to enter harbour. What is the effect on (i) The wave passing through the entrance? Less diffraction / spreading
The wave pattern after passing through the gaps for narrow gap formed circular waves and for wide gap formed plane wave The wavelength after pass through the gap remain the same for narrow and wide gap. b) Relate the size of the gaps, the waves patterns and the wavelengths to deduce a relevant physics concept.
(ii) The harbour? More damage to the harbour
Narrow gap produced circular wave while wider gap produced plane wave and the wavelength remain the same .
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. Physics Module Form 5
1.5 State the principle of superposition.
chapter 1 : Waves
GCKL 2011
ANALYSING INTERFERENCE OF WAVES The principle of superposition state when two waves overlap, the resultant displacement is equal to the sum of the displacements of the individual wave.
complete the diagram below.
2a
Constructive interference occur when a wave peak meets a wave peak.
Destructive interference. occur when a wave peak meets a wave trough.
.
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Complete the diagram 1.51 below with the i nformation given. R
S
Q P
Diagram 1.51 a.
Label P at a point of constructive interference.
b.
Label Q at a point of destructive interference.
c.
Draw the antinodal line and label it as R .
d.
Draw the nodal line and label it as S.
5. In constructive interference, the resultant wave is at maximum amplitude. 6. In destructive interference, the resultant wave is at
minimun
amplitude.
7. An antinodes line is a line joining all the points where constructive interference takes place. 8. An nodes line is a line joining all the points where destructive interference takes place.
Node line
Node line Node line
Diagram 1.52
Node line
Diagram 1.53
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
Question 9,10 and 11 based on diagram 1.52 and diagram 1.53. 9. The distance between consecutive antinodal lines ; x , in diagram 1.52 is shorter compare to diagram 1.53 10. The distance of between two coherent source; a, in diagram 1.52 is longer compare to diagram 1.53. 11. When the x is
shorter ( longer / shorter ) , the a is longer ( longer/ shorter.
12. The light interference experiment is also known as
Young’s double – slit experiment.
.
13. Diagram 1.54 show the interference pattern of a l ight wave.
Interference attern Diagram 1.54 Bright fringes in diagram 1.54 correspond to constructive interference Dark fringes in diagram 1.54 correspond to destructive interference 14. In the experiment set-up for the interference of sound wave, two loud speaker are connected to coherent source the common audio signal generator to produce
15. Diagram 1.55 show two loud speakers placed apart from each other. A person hears alternating loud and soft sounds as he walks along XY.
Diagram 1.55 The alternating loud and soft sounds i s caused by interference of the sound waves, wher the loud sound corresponds to the constructive interference and the soft sound corresponds to the destructive interference
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011
λ = ax D λ = wavelength, a = distance between two coherent source x = distance between two consercutive nodes ( or antinodes) D = perpendicular distance from the source and the position where x is measured. Worked example.
In a Young’s double-slit experiment, a light of wavelength 633 nm passes through two slits which are 0.5 mm apart. Vertical fringes are observed on a screen placed 4 m from the slits. a) Calculate the distance between two adjacent bright fringes. Solution; Answer : 5.1 mm
Two loudspeakers placed 2 m apart are connected to an audio signal generator that is adjusted to produce sound wave of frequency 550 Hz. The figure shows the detection of l oud and soft sound as a person moves along a line, 4.0 m from the loud speakers.
º
º 2.0 m
º
Loud sound Soft sound
4.8 m
º
º
4.0 m Calculate the : (a) Wavelength ( ans : 0.6 m) (b) Speed ( ans : 330 m s -1) of the sound wave.
information : a = 2 m, D = 4.0 m, x = 4.8 / 4 = 1.2 m f = 550 Hz
Solution : b) v = f λ, = 550 x 0.6 = 330 m s-1
(a) λ = ax /D = 2 x 1.2 = 0.6 m 1-19
. Physics Module Form 5
chapter 1 : Waves
1. Diagram 1.56 shows the interference pattern for water waves from two coherent source, S1 and S2.
GCKL 2011
Which diagram is correct when both waves meet?
Diagram 1.56 Which of the following shows the superposition of the waves at point Y? 4. Diagram1.54 shows two loudspeakers connected to an audio generator. Students are standing at position where loud sounds can be heard.
2. In which diagram will destructive interference occur when the wave meet?
A Diagram 1.54 (a) What type of wave is the sound waves? Longitudinal wave (b) Why are loud sounds heard by the students at that positions? Constructive interference takes place
C
(c) The distance between the two loudspeakers is 1.5 m. At 10.0 m from the loudspeakers, the distance between two adjacent rows of student is 4.0 m. Calculate the wavelength of this sound wave. λ = ax /D = 1.5 x 4 = 0.6 m 10
3. Diagram 1.57 shows two coherent wave propagate towards each other.
Diagram 1.57 1-20
. Physics Module Form 5
.
chapter 1 : Waves
5. Diagram 1.43 shows another modification to the harbour to overcome the heavy sea traffic problem. The wave pattern produced at the entrances is shown in diagram 1.43
GCKL 2011
White light source
Single slit Coloured filter
White screen
Double slit
Diagram 1.43
Diagram 1.43
Diagram 1.44
(i) The wave pattern formed is caused by the superposition of waves from two coherent sources. What is the meaning of coherent sources? Source that produded wave of the same freqyency and that in the same phase
Diagram 1.45 (ii) Describe a movement of two similar ship that are located at A and B. Explain your answer
a) What is meant by monochromatic light? Light with only one colour
b) Using the pattern of the fringes in figure 1.44 and 1.45, state two observation about the distance between consecutive fringes for the red light and blue light.
Ship at location A moves up and down with high amplitude Constructive interference occurs at A. The ship at B remain calm. Destructive interference occurs at B.
The distance between two consecutive fringes for the same light is equal. The distance between two consecutive fringes for red light is longet than blue light .
6. Diagram 1.43 shows the arrangement of c) Compare the wavelengths of red light t o blue light
apparatus for Young’s double slit. A white light source is passed through a coloured filter to produce a monochromatic light . Diagram 1.44 shows the pattern of the fringe formed on the screen when a red filter is used
The wavelengths of red light is longer compare to blue light.
The experiment is repeated by using a blue filter and the fringes formed are shown i n diagram 1.45 1-21
d) Compare the wavelengths of red light and blue light with the distances between consecutive fringes in (b) The greater the wavelengths the greater the distance between consecutive fringes.
. Physics Module Form 5
1.6
Describe sound waves
chapter 1 : Waves
GCKL 2011
ANALYSING SOUND WAVES
Sound waves are produced by vibration. Sound waves are .longitudinal waves. ( tranverse wave s/ longitudinal waves). Sound cannot be transmitted through a vacuum.. Loudness of a sound is dependent on its amplitude The louder the sound, the bigger the amplitude The pitch of a sound heard depends on the frequency The higher the pitch of the sound, the higher the frequency.
1.
Sound with frequency lower than 20 Hz is called infrasound
2. Sound with frequency higher than 20 000 Hz is called ultrasound. 3. Depth of the sea can be determine by using ultrasonic wave . The wave is sent by from the boat to the seabed. are detected by hydrophone next to the transmitter. The time is measured and the depth will be calculated.
Depth of sea , d = v x
Worked example 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 the freshwater is 1482 ms-1, calculate the depth of the lake. Information : v = 1482 ms -1 , t = 0.35 s
d=vx
= 1482 x (0.35/2) = 259.35 m
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. Physics Module Form 5
chapter 1 : Waves
1. A thin guitar string is strummed hard. It will produce a loud and high pitch sound. The most suitable graph to represent the above situation is 4
GCKL 2011
B. 1.2 x 10 6 m
D. 1.5 x 10 5 m
3. Diagram 1.64 shows a stretched steel wire which produces a loud sound when the wire is plucked.
Diagram 1.64 A loud sound means A. a high speed C. a high frequency B. a large amplitude D. a large wavelength 4. Which of the following corresponds to the highest pitch of sound?
2. Diagram 1.63 shows a submarine transmitting ultrasonic waves directed at a big rock on the sea bed. After 10 seconds, the subimarine detects the reflected wave.
Diagram 1.63 Calculate the distance of the submarine from the big rock. [ velocity of ultrasonic wave = 1 560 ms-1 ]
A. 3.9 km D. 31.2 km B. 7.8 km E. 156.6 km C. 15.6 km 3. A radar transmits a signal towards an aeroplane. The velocity if the signal is 3.0 x 108 ms-1. After 4.0 x 10-3 s, the radar detects the reflected signal. What is the distance of the aeroplane from the radar? A. 2.4 x 10 6 m C. 6.0 x 105 m
5. Two notes are played on a guitar. The second is louder and has a higher pitch. The second note is A higher in amplitude and lower in frequency B higher in both amplitude in frequency C lower in amplitude and higher in frequency D lower in both amplitude and frequency
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. Physics Module Form 5
chapter 1 : Waves
GCKL 2011 High pitch sound has high frequency and short wavelength. Frequency inversely proportional to wavelength. Sound is not diffracted to student A and B. Low pitch sound has low frequency and longer wavelength. The sound will diffracted better by the corner and all student can hear the sound clearly.
6. Diagram 1.65 shows an ultrasonic waves transmitted from a boat to the seabed to determine the depth, D, of the sea. The speed of the ultrasonic waves in water is 1 500 ms-1. The echo of the waves is received 2.0 s after the transmission.
(b) The depth of a sea is 90 m. A ship transmits an ultrasonic wave of frequency 50 kHz to the seabed and receives an echo 0.12 s later. Calculate: i) The speed of the ultrasonic wave in the water.
Diagram 1.65
d=vx What is the value of D? A. 375 m D. 3 000 m B. 750 m E. 6 000 m C. 1 500 m 7.
90 = v x (0.12/2) -1 V = 1500 ms (ii) The wavelength of the ultrasonic wave in the water. v = fλ λ = v / f 3 = 1.5x 10 4 5 x 10 -2 = 3 x 10 m
Diagram 1.65 shows an audio frequency generator connected to a speaker and placed near the corner of a wall. Three students, A,B and C are standing around the next corner. The generator and speaker can produce sound with the same speed but different pitch.
8. Diagram 1.66 shows an airport radar transmitting microwave signals. Microwave are transmitted to determine the position of aeroplane.
.
Diagram 1.65
a) State the physical quantity that affects the pitch of the sound. Frequency Diagram 1.66
(a) When a high pitch sound is generated, only student C can hear the sound clearly. When a low pitch sound is generated, all the three students can hear the sound clearly. Explain this situation.
a) Microwave are a type of electromagnetic wave.
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. Physics Module Form 5
chapter 1 : Waves
b) The radar transmits a signal at a velocity of 3.0 x 108 ms-1 towards the aeroplane P and detects the reflected signal 4.0 x 10 -4 s later. Calculate the distance of P from the radar transmitter at that time. d = d= =
GCKL 2011 (b) Explain why sonar used a high frequency sound wave. Ultrasonic waves can transfer more energy (c) If the time to detect the shoal of fish is 1/15 seconds, calculate the distance of the fishes from the boat if the speed of the sound waves in water is 1500 ms-1.
vt 2 3.0 x 108 (4.0 x 10-4) 2 60 000 m
d =
vt 2 = 1 500 x (1/15) 2 = 50 m
c) The radar detects the same signal after reflection by another aeroplane Q. The signal from Q arrives later than the signal from P.
(d) Explain why does the speed of sound in water is greater than the speed of sound in air? [2 m] because water is denser than air. The molecules are closer in water and it will travel faster.
(i) Compare the distance of P and Q from the radar. The distance of Q is further from radar compare to P.
(e) Name one application of sonar. ultra sound.
(ii) State how the difference of the distance of P and Q from the radar is determine any time. Determine the shortest distance from P to radar and from Q to radar.
9. The diagram below shows a fishing boat is detecting a shoal of fish by using a sonar system which has a high frequency sound wave.
.
(a) State the sound wave phenomenon for detecting the shoal of fish. Reflection
.
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. Physics Module Form 5
1.7 Describe the electromagnetic spectrum. list sources of electromagnetic waves
chapter 1 : Waves
GCKL 2011
ANALYSING ELECTROMAGNETIC WAVES
.
Electromagnetic spectrum consists of a group of waves with similar and arranged in increasing frequencies and decreasing wavelengths.
Radio waves : radio and television transmitter Microwaves : radar transmitter and microwaves oven. Infrared rays : sun Visible light : sun, LED, electric bulbs.. Ultraviolet rays : sun, sparks, mercury lamps..... X-rays : x-ray tubes Gamma rays : radioactive substance, cosmic rays.
describe the properties of electromagnetic waves
Fill in the box / blank with the correct answer. Long waves
t
Long waves
short waves
short waves
micro waves
micro waves
infra red Ultra violet X – rays gamma rays
infrared
Ultra violet
X – rays
gamma rays
1.
1.
consist of a group of waves with similar natures.
Electromagnetic spectrum
3. It is arranged in
increasing
4. Radio wave have the longest frequency waves.
frequencies and decreasing wavelengths .
( longest / shortest ) wavelength and low
( low / high)
5. Gamma rays have the shortest ( longest / shortest) wavelength and high ( low / high) frequency waves. 6. Electromagnetic waves consist of combination of oscillating ( interaction / oscillating) magnetic electric and ( force / magnetic) field perpendicular 7. Electromagnetic wave is a transverse
( transverse / longitudinal ) wave.
1-26
. Physics Module Form 5
8.
INFRARED RAY
chapter 1 : Waves
MICROWAVES
ULTRAVIOLET RAYS
Longest wavelength ( 106 – 10-1 m)
Used for broadcasting and communication
RADIO WAVES
X-RAY S
GCKL 2011
The range of wavelength is between 10 -3 – 10-6 m.
Also used in night vision devices.
Easily detected by human and animal eyes.
INFRARED RAY
Used in photography and can be transmitted through optical fibre
The range of wavelength is between 10 -6 – 10-9 m.
Can cause skin to tan and may result in skin cancer.
Can kill living cells,bacteria and germs.
The range of wavelength is between 10 -8 – 10-12 m.
Widely used in the medical field.
MICROWAVES
Ordinary ovens,grills and toaster use this wave to cook food. Can transmit information through the air to operate televisions and video recorders by remote control.
RADIO WAVES
Have shorter wavelength . ( 10 -1 – 10-3 m)
GAMMA RAY
Carries along wit it audio, video and other encoded information.
Suitable for satellite- based communication systems, mobile phone networks Military uses it for spying and surveillance.
VISIBLE LIGHT
Used to inspect metal castings and welded joints for hidden faults.
Shortest wavelength in the electromagnetic spectrum.
Used in radiotheraphy to treat cancer
Used sterillisation process
VISIBLE LIGHT
ULTRAVIOLET RAYS
X-RAY S
GAMMA RAY
1-27
Physics Module Form 5
GCKL 2010
1. Which of the following statements is true about electromagnetic waves? A. They are longitudinal waves. B. They are waves that require a medium to travel. C. The velocity of the waves is influenced by the wavelength D. They consist of both magnetic field and electric field. 2. What is the correct relationship between the wave length of an electromagnetic radiation and the energy it carries. Wave length
Energy carried
A. Short
High
B. Short
Low
C. Long
High
D. Long
Low
The content in the bag are examined by using A. X-ray C. Ultraviolet ray B. Gamma rays D. Infrared rays
5. Which is the correct arrangement of electromagnetic waves in order of increasing frequency? A. Infrared rays, Microwaves, Gamma rays, Ultraviolet rays. B. Gamma rays,, Ultraviolet rays, Infrared rays, Microwaves. C. Microwaves, Infrared rays, Ultraviolet rays, Gamma rays. D. Ultraviolet rays, Gamma rays, Microwaves, Infrared rays.
3. Diagram 1.7 shows an electromagnet spectrum.
6. Diagram 1.7
Figure 1.8 (a) shows the x-rays film of a patient. Figure 1.8 (b) shows the microwave from the satellite used in communication.
The waves at P,Q,R and S are A
B
C
D
P
Ultraviolet
X – ray
Microwave
X ray
Q
X –ray
Ultraviolet
Infrared
Microwave
R
Microwave
Infrared
Ultraviolet
x-ray
S
infrared
Microwave
X ray
microwave
4.
Figure 1.8 (a)
Figure 1.8
a) Observe the figures and state two similarities between the waves. Both are transverse waves/They transfer energy from one place to another/
At an airport, a passenger’s bag is placed in They can travel through vacuum with the speed of light.
the baggage scanner.
28
Physics Module Form 5
GCKL 2010
b) Which group does these two waves belong to? Electromagnetic waves c) Name one other wave that has the same properties. Radio waves / gamma rays / ultra violet / visible light / infra red 8
-1
d) Microwaves travel at a speed of 3.0 x 10 ms in a vacuum and have a frequency of 15 x 10 10 Hz. i)
Calculate the wavelength of these microwaves. λ = v/f =3.0 x 108 ms-1 15 x 1010 Hz. = 2.0 x 10-3 m.
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