U N
U N D E
D E R S
R S T A
T A N D
N D I N
I N G
G W
W A V
A V E S
E S
What is meant by a wavefront
What is meant by a wavefront An imaginary line that joins all the points on the An imaginary line that joins all the points on the crest of a wave.crest of a wave. State the direction of propagation of
State the direction of propagation of waves in relation to wavefronts waves in relation to wavefronts
The direction of propagation of a wave is
The direction of propagation of a wave is perpendicular to itsperpendicular to its wavefront.
wavefront. What is transverse wave?
What is transverse wave? A A transverse wave transverse wave is a is a wave wave in which particles of in which particles of the mthe mediumedium oscillate in the direction of the
oscillate in the direction of the propagation of the waves.propagation of the waves. Water waves
Water waves and andelectromagnetic waveselectromagnetic waves are examples of are examples of this type
this type of of waves.waves. What is longitudinal wave?
What is longitudinal wave? A longitudinal wave is a A longitudinal wave is a wave which the particles of the mediumwave which the particles of the medium oscillate in the direction parallel to the
oscillate in the direction parallel to the direction in which thedirection in which the wave moves
wave moves Sound waves
Sound waves is the example of this is the example of this type of waves.type of waves.
F
F ilil l il in the blank win the blank wi th thth th e ce corrorr eect ansct answewer r givegiven ben belowlow frequency
frequency period period Hertz Hertz ( ( Hz) Hz) amplitudamplitudee
1.
1. TheThe amplitudeamplitude of an oscillation is the maximum displacemof an oscillation is the maximum displacement for one ent for one completecomplete oscillation .
oscillation . 2.
2. TheThe periodperiod of the oscillation is of the oscillation is the time taken to the time taken to complete one oscillation.complete one oscillation. 3.
3. TheThe frequencyfrequency of the oscillation is the number of complete oscillation made in oneof the oscillation is the number of complete oscillation made in one second. The SI unit is
second. The SI unit is Hertz ( Hz)Hertz ( Hz) L
L abeabel thl th e e graph begraph below and filow and fi ll ll in in the bthe blank lank with with cocorrrr eect ansct answewerr ..
4.
4. In the diIn the displacemsplacementent
–
–
time graph as shown above, amplitude is r time graph as shown above, amplitude is r epresenteepresented by the d by the symbolsymbol ofof aa and period is represented by the symbol ofand period is represented by the symbol of TT
1.1
1.1
Displacement
5.
5. In the diIn the displacemsplacementent
–
–
distance graph as shown above, amplitude is represented by the distance graph as shown above, amplitude is represented by the symbol ofsymbol of aa and wavelength is represented by the symbol ofand wavelength is represented by the symbol of λ λ
6.
6. DampingDampingis occur when in an oscillating system when the systemis occur when in an oscillating system when the system losesloses ( gain /( gain / loses)
loses) energy energy to surrounding to surrounding in the in the form form ofof heatheat ( heat / ( heat / chemicachemical ) l ) energy.energy. 7.
7. The force responsible for damping is calledThe force responsible for damping is called dissipativedissipative ( ( equilibrium equilibrium / / dissipative) dissipative) forces.forces. 8.
8. In a simple pendulum, its natural frequency depending on itsIn a simple pendulum, its natural frequency depending on its lengthlength ( length /( length / mass ).
mass ). 9.
9. When an oscillating systems driven at its When an oscillating systems driven at its natural frequencynatural frequency, the system is , the system is said to be atsaid to be at reasonance
reasonance ( damping ( damping / / reasonancreasonance)e)
10.
10. A wave travels with a speed of 3.0 x 10A wave travels with a speed of 3.0 x 1088 ms ms-1-1
(a)
(a) What is the frequencWhat is the frequency of the wave if its wave length is 1.0 y of the wave if its wave length is 1.0 m?m? (b)
(b) Another wave Another wave is travelling with the is travelling with the same speesame speed but has a fred but has a frequency of quency of 1.5 1.5 x 10x 101212 Hz. Hz. What is the wavelength of the
What is the wavelength of the wave?wave? Solution. Solution. (a) (a) f =f = 3.0 x 103.0 x 1088 (b)(b) λ λ = v / f = v / f 1.0 1.0 ==3.0 x 103.0 x 1088 1.5 1.5 x x 10101212 = = 3.0 x 103.0 x 1088 Hz Hz = 2.0 x 10= 2.0 x 10 -4-4 m m Displacement
Displacement – – distance graph distance graph
Wave speed ,
S/c
2 4 6 l/cm
S/cm
t/s
2 4 6
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 graphsolution :
v = f λ, f = 1 / T
from (a) : T = 4 s, from (b) : λ = 4 cm
f = 0.25 Hz
v = f λ = 0.25 x 4 = 1 cm s-1
12.
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 Displacement/cm Distance/cm 1 2 5 -5 3
Practise 1.1 1.
Diagram 1.11
Base on the diagram 1.11 above, which distance represents the amplitude? 2. Diagram 1.12 shows how displacement
how varies with time.
Diagram 1.12 Which of the following is true?
Amplitude/ m Period / s Frequency / Hz
A 0 .1 0.50 2
B 0.2 0.50 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
5. Diagram 1.14 shows a wavefront pattern produces by a dipper vibrating at a frequency
of 12 Hz in a ripple tank.
Diagram 1.14
What is the speed of the waves? A. 2 cms-1 B. 8 cms-1 C. 12 cms-1 D. 18 cms-1 E. 36 cms-1
C 0.1 0.25 4
D 0.2 0.50 2
3. Diagram 1.13 shows the displacement-time graph of an oscillating system
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
9. Diagram 1.15 shows the cross section of water waves.
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
10.The graphs show the cross-sections of water waves. Which wave has the greatest energy?
11.Which graph represents a wave with amplitude of 4.0 cm and period of 0.05 s
11. Diagram 1.16 shows the displacement distance graph. The frequency of the wave is 5.0 Hz.
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.
Diagram 1.16
(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?
1.2
ANALYSING REFLECTION OF WAVES
.
1. complete the diagram 1.21 below to show the reflected waves.
Diagram 1.21 2. Fill in the box with the correct answer.
3. Draw the correct pattern of reflected water waves. wavefronts (a) reflector wavefronts (b) reflector Incidence ray Reflected ray i =incidence angle
r =r eflected angl e
(c)
(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 toangle of reflection Incident light ray
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?
3. Diagram 1.22 shows a sound wave reflected from a concrete wall.
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?
A. The wavelength of the incident wave is shorter than the reflected wave. B. The speed of the incident wave and the reflected wave is the same. C. The frequency of the incident wave is less than the reflected wave.
D. The angle of incident wave is greater than the angle of reflection of the reflected wave. Wavelength Magnitude of velocity
A. Unchanged Unchanged B. Increases Decreases C. Decreases Increases D. Increases unchanged Diagram 1.23 Diagram 1.22
6. 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?
7. Diagram 1.25 and Diagram 1.26 show the water and sound waves propagating towards a reflector.
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.
Norm Direction of reflected Reflect edwave Incident Diagram 1.25 i r E Stop watch Card board Diagram 1.26 Diagram 1.24
Analysing refraction of waves.
Describe refraction of waves in terms of the angle of incidence, angle of refraction, wavelength, frequency, speed and direction of propagation1. Waves can be refracted as they move from one medium ( volume / medium) to another.
2. When water waves travel from one area to another area of different depth, their speed changes ( remain / changes ) and the frequencyremain (remain / changes) .
3. The wavelength of waves in deep area is longer ( shorter / longer ) than that in the shallow area.
4. When waves travel from a denser medium to less dense medium , they refracted towards (away / towards) to normal.
Diagram 1.30
5. Diagram 1.30 shows the incident ray is refracted ... towards ( away / towards ) to normal.
Draw a diagram to show
refraction of wave
Complete the diagrams below.
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 depth of the sea parallel shallower
reduce refraction refracted wavefront
towards
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 benttowards 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 airnear ( 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
Practice 1.3
1. Diagram 1.34 shows water waves
propagating through a Perspex block in a ripple tank.
Diagram 1.4
Which wave pattern is observed when the waves pass through the perspex bloc.
2. Diagram 1.35 shows water waves
propagating in an area of different depths.
Diagram 1.35
Which of the following diagrams shows the propagation of the waves correctly?
3. When water waves pass from deep water into shallow water, how do the speed,
wavelength and frequency change?
Speed Wavelength Frequency A Increases Decreases No change B Decreases Increases Decreases C Increases Increases No change D Decreases Decreases 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
A the total internal reflection of light B the refraction of light
C the reflection of light D 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.
Which pattern of the wavefronts will be observed in the basin?
5. A ray of light passes from water to air. Which labeled arrow shows the direction of the ray in air?
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
Diagram 1.37 shows the waves formed on the screens.
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. (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
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.
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 1.38(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 .
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
ANALYSING DIFFRACTION OF WAVES
.
Describe diffraction of waves in terms of wavelength, frequency, speed, direction of propagation and shape of waves1. 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 islittle. 5. After diffraction, the frequencyremain unchange, the wavelength remain
unchange, and the speedremain unchange,
6. The direction of propagation of the diffracted waves changes. Draw a diagram
to show diffraction of waves
Complete the diagrams below.
1.4
Practice 1.4
1. Which of the following figure is true to show the diffraction of a water wave?
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 1.40
a) Observe Figure 1.40 compare the waves pattern and the wavelength of the waves
after they pass through the gaps. 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.
Narrow gap produced circular wave while wider gap produced plane wave and the wavelength remain the same.
3. Diagram 1.42 shows waves moving towards a harbour.
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.
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 (ii) The harbour?
ANALYSING INTERFERENCE OF WAVES
State theprinciple of superposition.
The principle of superposition statewhen two waves overlap, the resultant displacement is equal to the sum of the displacements of the individual wave.
complete the diagram below.
Constructive interference occur when a wave peak meets a wave peak.
Destructive interference. occur when a wave peak meets a wave trough.
.
1.5
Complete the diagram 1.51 below with the i nformation given.
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 asR . 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.
Diagram 1.52 Diagram 1.53
Node line Node line
Node line Node line P R Q S
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.
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 the common audio signal generator to produce coherent source
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 is caused byinterference of the sound waves, wher the loud sound corresponds to the constructive interference and the soft sound corresponds to the
destructive interference
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.
Calculate the :
(a) Wavelength ( ans : 0.6 m) information : (b) Speed ( ans : 330 m s-1) a = 2 m, D = 4.0 m,
of the sound wave. x = 4.8 / 4 = 1.2 m
f = 550 Hz Solution : (a) λ = ax /D b) v = f λ, º º º º Loud sound º Soft sound 2.0 m 4.0 m 4.8 m
1. Diagram 1.56 shows the interference pattern for water waves from two coherent source, S1 and S2.
Diagram 1.56
Which of the following shows the superposition of the waves at point Y?
2. In which diagram will destructive interference occur when the wave meet?
3. Diagram 1.57 shows two coherent wave propagate towards each other.
Diagram 1.57
Which diagram is correct when both waves meet?
4. Diagram1.54 shows two loudspeakers connected to an audio generator. Students are standing at position where loud sounds can be heard.
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) 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
A
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
Diagram 1.43
(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
(ii) Describe a movement of two similar ship that are located at A and B.
Explain your answer
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.
6. Diagram 1.43 shows the arrangement of
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 experiment is repeated by using a blue filter and the fringes formed are shown in
. White light
source Single slit
Coloured filter White screen Double slit Diagram 1.43 Diagram 1.45 Diagram 1.44
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.
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. c) Compare the wavelengths of red light t o
blue light
The wavelengths of red light is longer compare to blue light.
d) Compare the wavelengths of red light and blue light with the distances between
consecutive fringes in (b)
ANALYSING SOUND WAVES
Describe sound
waves Sound waves are produced byvibration.
Sound waves are .longitudinal waves. ( tranverse wave s/ longitudinal waves). Sound cannot be transmitted through avacuum..
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 calledinfrasound 2. Sound with frequency higher than 20 000 Hz is calledultrasound.
3. Depth of the sea can be determine by usingultrasonic 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 = v x
= 1482 x (0.35/2)
= 259.35 m
1.6
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
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
B. 1.2 x 10 6m D. 1.5 x 105 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?
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
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.
Diagram 1.65 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. 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.
. Diagram 1.65
a) State the physical quantity that affects the pitch of the sound.
Frequency
(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.
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.
(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.
d = v x
90 = v x (0.12/2)
V = 1500 ms
-1(ii) The wavelength of the ultrasonic wave in the water. v = fλ λ = v / f = 1.5x 103 5 x 104 = 3 x 10-2 m
8. Diagram 1.66 shows an airport radar
transmitting microwave signals. Microwave are transmitted to determine the position of aeroplane.
Diagram 1.66
a) Microwave are a type of electromagnetic wave.
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 = vt 2
d = 3.0 x 108 (4.0 x 10-4) 2
= 60 000 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.
(i) Compare the distance of P and Q from the radar.
The distance of Q is further from radar compare to P.
(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.
(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. d = vt 2 = 1 500 x (1/15) 2 = 50 m
(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.
(e) Name one application of sonar. ultra sound.
ANALYSING ELECTROMAGNETIC WAVES
.
Describe theelectromagnetic spectrum.
Electromagnetic spectrum consists of a group of waves with similar and arranged in increasing frequencies and decreasing wavelengths.
list sources of electromagnetic waves
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 short waves micro waves infra red Ultra violet X – rays gamma rays
t 1.
1. Electromagnetic spectrum consist of a group of waves with similar natures. 3. It is arranged in increasing frequencies anddecreasing wavelengths .
4. Radio wave have the longest ( longest / shortest ) wavelength and low ( low / high) frequency waves.
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) electric and magnetic (force / magnetic) field perpendicular
7. Electromagnetic wave is a transverse ( transverse / longitudinal ) wave.
1.7
Longwaves gamma
rays X –
rays
8. INFRARED RAY MICROWAVES RADIO WAVES VISIBLE LIGHT
ULTRAVIOLET RAYS X-RAY S GAMMA RAY
Longest wavelength ( 106
–
10-1 m) Used for broadcasting and communication RADIO WAVES
Carries along wit it audio, video and other
encoded information.
Have shorter wavelength . ( 10-1
–
10-3 m) Suitable for satellite- based communication systems,
mobile phone networks
Military uses it for spying and surveillance. MICROWAVES
The range of wavelength is between 10-3
–
10-6 m. Ordinary ovens,grills and toaster use this wave tocook food.
Can transmit information through the air to operate
televisions and video recorders by remote control.
Also used in night vision devices. INFRARED RAY
Easily detected by human and animal eyes.
Used in photography and can be transmitted through VISIBLE LIGHT
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. ULTRAVIOLET RAYS
The range of wavelength is between 10-8
–
10-12 m. Widely used in the medical field. Used to inspect metal castings and welded joints for hidden X-RAY S
faults.
Shortest wavelength in the electromagnetic spectrum. Used in radiotheraphy to treat cancer
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
3. Diagram 1.7 shows an electromagnet spectrum.
Diagram 1.7
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.
At an airport, a passenger’s bag is placed in
the baggage scanner.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.
6. 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.
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/
They can travel through vacuum with the speed of light.
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
d) Microwaves travel at a speed of 3.0 x 108ms-1in a vacuum and have a frequency of 15 x 1010Hz.
i) Calculate the wavelength of these microwaves.
λ = v/f
=3.0 x 108ms-1 15 x 1010Hz. = 2.0 x 10-3 m.
