chapter 6 2010- waves

Introduction

A wave is produced by a source of vibration.

Mechanical waves need a material medium or their propagation.Examples of mechanical waves include water waves ,sound waves, shock waves as in earthquakes and waves in strings, springs and rods.Electromagnetic waves do not need a material medium for their propagation. Examples of electromagnetic waves are radio waves , light waves , infra-red (IR) and ultra-violet ( UV).

As a wave travels through a medium, there is no transfer of matter but only transfer of energy from a vibrating source.Common terminology of vibrations

Vibration:A periodic motion where the system performs a repeated to-and-fro motion about an equilibrium position.Equilibrium position:The position of the object where is no resultant force acts on the object. One oscillation:

To-and-fro motion from the equilibrium position.

Amplitude :The maximum displacement of the objects from their equilibrium position.Period, T

The time taken for one complete oscillation.The S.I. unit is second (s)

t = time n = number of oscillationsFrequency, fThe number of complete oscillations per second.The S.I. unit is Hertz (Hz)

Or

Graph displacement-time

Example 1

A pendulum makes 20 complete oscillations in 24.0 s.

Calculate

(a) the period (b)the frequency Solution

Example 2

Based on he graph above, determine the

(a) amplitude (b) period

(c) frequencySolution

Natural Frequency:The frequency of the free oscillation of a system without any external forces are exerted to the system.Factors affecting the natural frequency of the vibration systems.Vibration systemFactors affectingFormula

Oscillation of a pendulum

Oscillation of a spring hang with a mass

Oscillation of a jigsaw blade fixed with plasticine

Transformation of energy in a vibration system

What is meant by ResonanceA phenomenon that a system vibrates with a maximum amplitude.

It occurs when the frequency of the system same as its natural frequency. Experiment to show a phenomenon of resonance The pendulum B ( driver pendulum) is pulled well aside an released so that it oscillates in plane perpendicular.

All the pendulums oscillate but with different amplitudes.

The pendulum D whose length equals that of the driver (pendulum B) has the greatest amplitude because its natural frequency of oscillation is the same as the frequency of the driving pendulum. Examples of Resonance in Everyday Life

Example 1: A car or a washing machine may vibrate quite violently at particular speeds. In each case ,resonance occurs when the frequency of a rotating part ( motor, wheel, drum etc.) is equal to a natural frequency of vibration of the body of the machine. Resonance can build up a vibration to a large amplitude.Example 2: The story is told of an opera singer who could shatter a glass by singing a note at its natural frequency.Example 3:

The wind ,blowing in gusts, once caused a suspension bridge to sway with increasing amplitude until it reached a point where the structure was over-stressed and the bridge collapsed.Example 4:

Wind instruments such as flute, clarinet, trumpet etc. depend on the idea of resonance. Longitudinal pressure waves can be set up in the air inside the instrument. The column of air has its own natural frequencies at which it can vibrate. When we blow, we use the mouthpiece to start some vibrations. Those which happen to match exactly the natural frequencies of the instrument are picked out and magnified.Example 5 :The another example of useful resonance is the tuning circuit on a radio set. Radio waves of all frequencies strike the aerial and only the one which is required must be picked out. This is done by having a capacitance-inductance combination which resonates to the frequency of the required wave . The capacitance is variable; by altering its value other frequencies can be obtained.Example 6 :

Microwave ovens use resonance. The frequency of microwaves almost equals the natural frequency of vibration of a water molecule. This makes the water molecules in food resonate . This means they take in energy from the microwaves and so they get hotter. This heat conducts and cooks the food.

Example 7 :

The picture showing the insides of the body was produced using magnetic resonance imaging (MRI). Our bodies contain a lot of hydrogen , mostly in water. The proton in a hydrogen spins . A spinning charged particle has a magnetic field, so the protons act like small magnets. These are normally aligned in random directions. Placing a patient in a strong magnetic fields keeps these mini magnets almost in line. Their field axis just rotates , a bite like a spinning top. This is called precessing.Damping

Damping is a word used to describe how movement and vibrations are reduced or slowed down.

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

When a system is damped , the amplitude of the of oscillation decreases slowly until the system stops oscillating.Damping is usually caused by external frictional forces such as air resistance . It can also be caused by internal forces , where energy is lost from the system in form of heat.

In daily use ,e.g. shock absorbers in cars cause oscillations to die down after a car has gone over a bump in the road.For another example, damping is introduced intentionally in measurement instruments such as galvanometer , spring balance etc. to overcome the problem of taking a reading from an oscillating needle. 1The figure shows a bob of a simple pendulum is swinging between point A and point C.

One oscillation is counted when it oscillating fromAA to B

B A to C

CA to C and back C to B

DA to C and back C to A

2The figure shows a bob of a simple pendulum is swinging between point P and point Q. It takes 13.8 s to swing from P to Q and back to P twenty times

What is the period of the pendulum?

A0.69 s

B1.38 s

C1.45 s

D27.6 s

3The figure shows a pendulum is swinging. The time taken from the rest position M to its maximum displacement N is 2.0 s.

What is the period of the pendulum?

A2.0 s

B4.0 s

C6.0 s

D8.0 s

4A child on a swing makes 20 complete swings in 30 seconds.

What is the frequency of the oscillation?

A

Hz

B

Hz

C

Hz

D

Hz 5

Base on the figure above, which distance represents the amplitude?6The diagram shows how displacement varies with time. Which of the following is true?Amplitude/ m Period / s Frequency / Hz

A0 .1

0.50 2

B0.2

0.50 1

C 0.1 0.25 4

D 0.2 0.50 27The period of oscillations of a simple pendulum increases when the ________________________ increases.

Alength of the pendulum

Bmass of the bob of the pendulum

Cacceleration due to gravity

Damplitude of the oscillations of the pendulum

8The figure shows P,Q,R and S are four pendulums of different lengths and masses of the bob.

Which pendulum swings the slowest?

AP

BQ

CR

DS9Pak Abu has a pendulum clock as shown in the diagram below.

Every day it was observed that the clock was slow about 2 minutes.

To correct the clock Pak Abu

Araised the position of the bob

Blowest the position of the bob

Cincreased the mass of the bob

Ddecreased the mass of the bob

10The figure shows a simple pendulum.

Which of the following is true?

AThe amplitude of oscillation is 20 cm

BThe period of oscillation is the taken to move from A to C

CThe frequency of oscillation increases when the length of pendulum decreases

11Which of the following arrangements of springs produces the highest frequency?

[ All the springs are identical ] 12A spring is loaded with a weight of 40 g takes 0.6 s to make a complete swing. What is the time of a complete swing of the spring , when the spring is carried out to the surface of the Moon?

( g earth = 1 g moon )

6

A0.1 s

B 0.6 s

C3.6 s

D4.2 s

13The vibration frequency of a piece of jigsaw blade with plasticine ball at its end is not depends on

Athe length of the jigsaw blade

Bthe stiffness of the jigsaw blade

Cthe mass of the plasticine ball

Dthe acceleration due to gravity14 What energy changes take place when a load hang at the end of a spring is displaced downwards and released to make vertical vibrations?AGravitational Potential Energy ( Kinetic energy ( Elastic Potential EnergyBKinetic energy( Gravitational Potential Energy ( Elastic Potential EnergyCGravitational Potential Energy ( Kinetic energy ( Gravitational Potential Energy

DElastic Potential Energy ( Kinetic energy ( Elastic Potential Energy

15The figure shows a pendulum is swinging.

At which point does the bob of the pendulum have both of kinetic energy and gravitational potential energy?16The figure shows a simple pendulum of length 40 cm.A metal rod R is clamped at R to make OR = 20 cm.

Which of the following is not true when the bob is displaced and released ?

AAt point B ,the bob has the highest velocityBThe time taken to move from to A to B same as from B to C. CThe gravitational potential energy at A same as at CDThe gravitational potential energy at A same as the kinetic energy at B

17The figure shows five pendulums that are hung from the wire MN. The pendulum P is displaced and released.

Which of the pendulums will oscillate with the highest amplitude?

APendulum W

BPendulum X

CPendulum Y

DPendulum Z

18Which of the following physical quantities has a maximum value when resonance occurs?

Afrequency

Bperiod

Camplitude

Dacceleration19A spring vibrates at a natural frequency 50 Hz. Resonance occurs when the frequency of forced vibrations on the spring is

A0 Hz

B25 Hz

C50 Hz

D100 Hz

20The figure shows the arrangement of the apparatus to show the phenomenon of resonance but the resonance not occurs.

To improve the experiment ,Athe pendulums are oscillated with a maximum speedBthe iron rod is replaced by a string

Cincrease the mass of the bobs

21Which of the following phenomenon is not caused by resonance ?AThe violent vibrations of a washing machine at some spin speeds BThe tuning circuits in TV and radio sets work at the frequency of the station you select CThe wind instruments produce sound by forcing the air inside the tubeDThe shock absorbers in cars cause oscillations to die down after a car has gone over a bump in the road

22A system is oscillating at its natural frequency without damping.

What happens to the total energy of the oscillating system?

AIt remains constant

BIt decreases

CIt increases

23As the amplitude decreases the ______________ decrease.

Aperiod

Bfrequency

Cenergy

Dnumber of

oscillations24The figure shows a mass hanging from a spring is immersed in water.

Which of the following graph shows the vibrations the spring ?

25The figure shows a paper cone filled with water attached to spring. The paper cone has a hole at its end.

Which of the following graph shows the vibrations the spring while the water droplet drop from the hole? 26Diagram shows a simple pendulum which consists of a bob of mass 40.0 g at the end of a light inelastic string of length 20.0 cm. The pendulum makes 20 complete oscillations in 5.0 s.

(a) By using the letters A,B and C in the diagram above state the (i) equilibrium position

...........................................................

(ii)the meaning of period

..(b)What is the frequency of the oscillations of the pendulum ?

(c)What is the frequency of the oscillations of the pendulum when a bob of mass 50.0 g is used? (d)What happens to the frequency of the oscillations of the pendulum when the length of the pendulum is 80.0 cm ?

............................................................................(e)After a while the pendulum stops to oscillate .

(i) Explain why?

...................................................................

...................................................................

(f)Plot a graph displacement time to show why the pendulum stops to oscillate. (g) State the form of energy when the pendulum

(i) at B

............................................................

(ii) between B and C

............................................................27 Diagram 27 shows a trolley rests on a horizontal frictionless surface and is connected to two walls by two steel springs. The trolley vibrates with its natural frequency when it is pulled aside and released.

Diagram 27

(a) What is meant by the natural frequency ?

............................................................................(b) What will happen to the nature frequency of the

both springs when

(i)the steel springs are replaced by the cooper springs.

............................................................

(ii)the number of trolley is increased.

............................................................(iii)the experiment is conducted at the surface of the Moon.

............................................................(c)When the amplitude of the vibrations remain constant, draw, using the same axes shown below, two displacement- time graphs to compare the vibrations of the springs with one trolley and then with two trolleys are used. 28A student carries out an experiment to find out the relationship between mass, m and the oscillation period, T of a piece of jigsaw blade. The jigsaw blade is clamped at one end and a plasticine ball with mass, m is fixed at the other end as shown in Diagram 28

Diagram 28

The jigsaw blade is displaced horizontally to one side and then released so that it oscillates. The time for 20 oscillations ,t is taken by a stop watch. The experiment is repeated by using plasticine balls with different masses.The results of the experiment are shown in the table below.Mass,

m /k gTime for 20

oscillations, t / sPeriodT / sT2 / s2

0.128.0

0.240.0

0.350.0

0.456.0

0.564.0

0.670.0

(a) Complete the table above.

(b) Base on the graph paper above plot a graph T2 against m.

(c)Based on your graph state the relationship between T and m.

.....................................................................

(d) Determine the value of

(i) m when T = 2.2 s

(ii) T when m = 0.72 kg.

(e)State one precaution that should be taken during this experiment.

..29Each figure below shows a boxer punches the punch-ball with two different sizes. The big punch-ball vibrates more slowly than the small punch-ball.

Observe the vibrations of each of the punch-ball.

Based on the observations:

(a) State one suitable inference that can be made.

(b) State one appropriate hypothesis for an investigation.

(c) With the use of apparatus such as spring, slotted mass and other apparatus , describe an experimental framework to test your hypothesis.

In your description , state clearly the following:

(i)Aim of the experiment

(ii)Variables in the experiment

(iii)List of apparatus and materials

(iv) Arrangement of the apparatus

(v) The procedure of the experiment

which include the method of controlling the manipulated variable and the method of measuring the responding variable.

(vi)Way you would tabulate the data

(vii)Way you would analysis the data

Introduction

Oscillations can produce waves. Waves transfer energy from one place to another without permanently displacing the medium through which they travel.

When we drop a stone into a pond, the kinetic energy of the stone makes the water surface move up and down near where the stone lands; ripples spread out outwards and if an floating object on the water some distance away will start to bob up and down. It is becaused the original energy of the moving stone has been transferred to the object by the wave motion on the water surface.

When we are at the seaside, we can see large as well as small waves reaching the shore. These waves arise because of the strong winds in the middle of the sea.The energy of the winds is carried by the waves to the shore. The water from the middle of the sea does not reach the shore.

The wave motion is regular and repetitive (i.e. periodic motion)

There are two main types mechanical waves such as sound waves and electromagnetic waves.

Transverse waves

Waves in which the direction of vibration of the particles is perpendicular to the direction of wave propagation called a transverse wave.

The examples of transverse waves are water waves and electromagnetic waves (radio waves ,microwaves , infra-red (IR) light waves , ultra-violet ( UV), X-rays and gamma

rays )

Longitudinal waves

Waves in which the direction of vibration of the particles is parallel to the direction of wave propagation called a longitudinal wave.

An example of transverse waves is sound waves.

Wave terminology

Amplitude:

The maximum displacement of the medium particles from the equilibrium position.

Period , T:

The time for one complete oscillations of each particle in the wave.

Frequency, f :

The number of oscillations of each particle in the wave in one second.

Wavelength , The distance between two consecutive points which are vibrating in phase.

Or

The distance from one wave crest to the next.

Or

The distance from one wave trough to the next.

Or

Wavespeed , v

The distance moved by a wave in one second.

The wavespeed depends only the medium the waves are traveling through.

Wavefront

The locus of points which vibrates in phase.

For water waves there are two types of wavefront i.e circular wavefront and plane wavefront.

Crest

The point where a wave causes maximum positive displacement of the medium.

Trough

The point where a wave causes maximum negative displacement of the medium

Compression

Region along a longitudinal wave where the pressure and density of particles are higher than when no wave is passing.

Rarefaction

Region along a longitudinal wave where the pressure and density of particles are lower than when no wave is passing

The wave equation

Example 1

A student moves the end of a long spring from side to side 4 times per second . The wavelength of the wave on the spring is 0.6 m. With what speed do the waves moves along the spring?

Solution

Example 2

Radio waves travel at a speed 3 x 108 ms-1. What is the wavelength of FM radio waves received at 200 MHz on your radio dial?

Solution

Example 3

A long rope is stretched out on the floor. One end of the rope is then shaken. The graph shows the rope at a particular moment in time. The rope vibrated at a frequency 8 Hz.

Determine

(a) the amplitude

(b) the wavelength

(c) the speed

Solution

Example 4

The figure shows the sound waves produced by a tuning fork.

(a)Base on the figure determine,

(i) the amplitude

(ii)the wave length

(b)What is the frequency of the sound if the speed of sound is 330 ms-1.Solution

Waves on water- Ripple tank

In laboratory, to produce water wave we use a ripple tank.

A shallow tray of clear plastic holds the water, and a light above the water surface projects the wave patterns on a sheet of white paper on the bench below the tank.

The bright and dark bands of the wave pattern formed on the screen because the surface of water acts as lenses.

The crest of water waves similar with convex lens and the trough of water waves similar with concave lens.

Plane waves are produced by a straight bar which hangs by two elastic bands from supports near one end of the tank.

Circular waves are produced by using dippers fixed to the bar.

When a continuous stream of waves is used , it is sometimes easier to see by using a mechanical stroboscope to freeze the wave pattern. When the frequency of the waves same as the frequency of the stroboscope the pattern will appear stationary.

Stroboscope frequency = number of slits x rotation

frequency of stroboscope

or

Example 5

A mechanical stroboscope has 8 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 12 cm. Calculate the speed of the water waves.

Solution

Determination of wavelength in ripple tank

The a.c.power supply is switched on to vibrate the motor.

The stroboscope is rotated until the waves freeze.

The distance between 10 consecutive bright bands in measured on the screen , L

The wavelength is calculated , = L 10

1Which of the following is the transverse wave different from the longitudinal wave?

Aspeed

Bperiod

Camplitude

Ddirection of vibration of the particles and direction of wave propagation

2The figure shows a cork floating in a water tank.

Which figure shows the movement of the cork when the wave passes?

3The figure shows a slinky spring is moved backwards and downwards to produce a model of a wave.


Type of wavedirection of the wave propagation

compare with the spring vibration

ALongitudinal

Parallel

BLongitudinal

Perpendicular

CTransverse

Parallel

DTransverse

Perpendicular

4In which of the following pairs is the first wave motion transverse and the second wave motion longitudinal?

Transverse

Longitudinal

ALight

Radio

BInfra-red

Ultra-violet

CX-ray

Sound

DMicro

Ripples

5The figure shows a cross-section of a water wave.

Which points are one wavelength apart?

AP and R

BQ and S

CQ and T

DP and T

6 The figure shows a model of a wave produce by

a slinky spring.

What is the wavelength ?

A15 cm

B30 cm

C45 cm

D60 cm7

Based on the figure above , which of the following is true?

AmplitudeWavelength

A6 cm8 cm

B6 cm11 cm

C3 cm8 cm

D3 cm11 cm

8The figure shows a wavefront pattern produced by a dipper vibrating at a frequency of 12 Hz in a ripple tank.

What is the speed of the waves?

A2 cm s-1

A8 cm s-1

C12 cm s-1

D18 cm s-19A dolphin emits an ultrasonic wave with a wavelength of 0.01 m. The speed of ultrasonic wave in water is 1 500 ms-1.

What is the frequency of the ultrasound?

A1.5 x 101 Hz

B3.0 x 101 Hz

C1.5 x 105 Hz

D3.0 x 105 Hz

10The figure shows a transverse wave is produced a long rope by a student. The students hand make 10 complete up and down movements in 1.0 s

What is the speed of the wave?

A0.5 ms-1

B2.0 ms-1

C4.0 ms-1

D10 ms-1

11The diagram shows the straight lines represent the positions , at one instant , of successive crests of plane waves traveling on water. The waves travel at distance 45.0 cm in 3.0 s.

What is the frequency of the water waves?

A30 Hz

B15 Hz

C7.5 Hz

D2.5 Hz

12A 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. Calculate the speed of the water waves.

A60 cms-1

B120 cms-1

C180 cms-1

D240 cms-1

13Which graph shows the relationship between frequency, f and wavelength , of a wave?

14A dipper moving up and down makes waves in a ripple tank.

What will happen when the dipper frequency is decreased?

AThe waves will be far apart each other

BThe waves will be closer together

CThe wave peaks will be higher and the troughs lower

D The wave peaks will be lower and the troughs higher

15A vibrator produces a water wave vibrates 20 vibrations per second. When the frequency of the vibrator is increased by 2 times , what happen to the wavelength of the water wave?

A of its initial wavelength

Bsame as its initial wavelength

C2 times of its initial wavelength

D4 times of its initial wavelength

16A water wave of wavelength 6 cm travels with a speed 12 cm s-1 from deep water to shallow water. At the shallow water the speed of the wave is 20 cm s-1. What is the wavelength of the wave at shallow water?

A8 cm

B10 cm

C12 cm

D16 cm

17The figure shows a loudspeaker produces a sound with a frequency 300 Hz


AThe transverse wave is produced

BX is a rarefaction region

CThe wavelength is 1.2 m

DThe speed of the sound is 250 ms-1

18The figure shows a graph displacement- time of water waves.


AThe period of the water wave to vibrating is 25 s

BThe amplitude of the water wave is 0.4 m

CThe frequency of the water wave is 0.05 Hz

DThe wavelength of the water wave is 20 m 19Diagram 19 shows a longitudinal wave produced by a slinky spring.

Diagram 19(i) What is a longitudinal wave?

..............................................................................

(ii) What are P and Q ?

P :......................................................

Q : ..................................................... (iii) What is the wavelength of the wave 20Diagram 20 shows a graph displacement-distance for a transverse wave.

Diagram 20

(a) On diagram 20 ,mark(i) the direction of vibration of the particles and the direction of wave propagation .

(ii)two points vibrate in phase.

(b) Give one example of the transverse wave .

.....................................................................

(c) Determine

(i) the amplitude

(ii) the wavelength

(d) What is the speed of the wave when the frequency is 25 Hz.

(f)Give one example of the natural phenomenon to show that a wave transfer energy.

............................................................................

............................................................................21Diagram 21 shows a student setting up waves on a long elastic cord . The students hand makes 5 complete up-and -down movement in 2. 5 s, and in each up-and-down movement the hand moves through a height of 0.4 m.

P , Q, R, S and T are the points marked on the cord.

Diagram 21(a) What type of wave is produced by the cord?

(b) State two points that out of phase.

(c) Determine

(i)the amplitude

(ii) the frequency

(iii) the speed of the wave

(d)What happens to distance of PR when frequency of the waves increase?

22Diagram 22 shows a ripple tank is set up to produce a water wave.

(a)Explain why

(i)the depth of water in ripple tank be uniform throughout?

.

.

(ii)the inner surface of the ripple tank is lined with a layer of sponge?

(b)Draw a ray diagram in the and indicate the positions of the bright and dark bands in the figure above.

(c)A mechanical stroboscope has 4 slits and rotates at a frequency 5 Hz. The stroboscope is used to observe the water waves. The observer notes there are 6 successive bright bands at a distance 12 cm. Calculate the speed of the waves.

Introduction

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

The reflection of waves obeys the law of reflection :

(a) The angle of incidence is equal to the angle of reflection.

(b) The incident wave, the reflected wave and the normal lie in the same plane.

Velocity, vFrequency ,fWavelength, (Angle

unchangedUnchangedUnchangedi = r

To investigate the reflection of water waves a metallic plane reflector is placed at the centre of a ripple tank. The motor with a wooden bar attached is switched on to produce plane waves which propagate towards the reflector. The reflector repositioned to produce different angles of incidence.

The following figure shows two examples pattern of the reflection of the water waves.

(a)

(b)

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a water wave.

Hypothesis:

The angle of reflection increases as the angle of incidence increases.

Aim of the experiment :

To investigate the relationship between the angle of incidence and the angle of reflection.

Variables in the experiment:

Manipulated variable: Angle of incidence

Responding variable: Angle of reflection

Constant variable: depth of water in ripple tank

List of apparatus and materials:

Ripple tank, lamp, motor ,wooden bar , power supply white paper , protractor ,plane reflector and mechanical stroboscope.

Arrangement of the apparatus:

The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.

The power supply is switched on to produce plane waves which propagate towards the reflector.

The incident waves and the reflected waves are freeze by a mechanical stroboscope.

The waves are sketched on the screen.

By using a protractor , the angle of incidence is measured = i and the angle of reflection = r

The experiment is repeated 5 times for the other angles of incidence.

Tabulate the data:

i

r

Analysis the data:

Plot the graph r against i

Reflection of light waves

When rays of light strike any surface the rays are reflected , unless the surface is black, when they are absorbed.

The reflection depend on how smooth the surfaces are. Good mirrors reflect well over 90% of the light that reaches them, with only a small amount being absorbed.

A plane mirror is a flat smooth surface which reflects regularly most of the light falling on it.

The phenomenon of reflection of light obeys the law

of reflection.

(a)The angle of incidence is equal to the angle of reflection.

(b)The incident wave, the reflected wave and the normal lie in the same plane.

It also can be seen that

(a) The size of the image = the size of the object

(b) The distance of the image = the distance of the object

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a light wave.

Hypothesis:







Constant variable: position of the plane mirror


Ray box, plane mirror, plasticine, protractor and white paper

Arrangement of the apparatus


A normal line ,ON is drawn on the white paper.

A ray of light from the ray box is directed to the plane mirror.

By using a protractor , the angle of incidence is measured = i and the angle of reflection = r


Tabulate the data:

i

r

Analysis the data:


Reflection of sound waves

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

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

The experiment to investigate the relationship between the angle of incidence and the angle of reflection of a sound wave.

Hypothesis:







Fixed variable: the position of stop watch from the smooth wall.


Cardboard tube, soft wood , stop watch, protractor and smooth wall.



By using a protractor , the angle of incidence is measured = i

The stopwatch is started.

The cardboard tube B is moved around until the watch can be heard most clearly.

By using the protractor , the angle of reflection is measured = r


Tabulate the data:

i

r

Analysis the data:


1The figure shows a set of a plane waves arriving at a plane reflector placed in a ripple tank.

Which figure shows correctly the reflected waves?

2Which diagram shows how water waves would be reflected by a plane barrier?

3Which figure shows the correct pattern of reflected water waves?

4Diagram shows plane water waves travelling towards an L-shaped barrier in a ripple tank.

Which diagram shows the reflected wave pattern?

5The figure shows a set of a plane waves arriving at a plane reflector placed in a ripple tank.

Which of the following will change?

Awavelength

Bspeed of wave

Cwave direction

Dfrequency of

wave

6The diagram shows a single ray of light being directed at a plane mirror.

What are the angles of incidence and reflection?

Angle of

Angle of

incidence

reflection

A 35o

55o

B 55o

35o

C 35o

35o

D 55o

55o7The diagram shows a mirror is titled at an angle of 50o to the bench. A ray of light is directed so that it hits the mirror at an angle of 20o to the surface of the mirror.

What is the angle of reflection?

A20o

B40o

C50o

D7008The figure shows two mirrors X and Y inclined to each other at 900 . A ray of light falls upon miror X.

What is the value of the angle of the incidence upon mirror Y ?

A15o

B30o

C45o

D6009Diagram shows a ray of light being reflected by a plane mirror PQ. The mirror is then rotated 10 anticlockwise.

What is the new angle of reflection of the ray of light?

A20(

B30(

C40(

D50(10The figure shows 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 stopwatch is heard? 11Echo is a phenomenon caused by

Athe refraction of sound waves

Bthe reflection of sound waves

Cthe diffraction of sound waves

Dthe polarization of sound waves

12The figure shows a sound wave is reflected from a brick wall.

Compared with the incident wave, the reflected wave has

Aa greater amplitude

Ba shorter wavelength

Cthe same speed

Dthe same velocity

13Diagram 13.1 shows plane water waves is produced by a vibrating wooden bar vibrates at a rate 15 waves per second.

Diagram 13.1

(a)On Diagram 13.1,(i)mark the direction of the propagation of the water waves.

(ii)determine the wavelength of the waves.

(iii)calculate the speed of the water waves.

(b)A plane reflector is placed at different inclined angle in front of the water waves as shown in Diagram 13.2. Draw the pattern of the reflected wave in the Diagram 13.2(i)

(ii)

Diagram 13.2

14 Diagram 14 shows a photograph of reeds growing

in a pond. The image of the reeds can be seen in the water. Diagram 14Based on the observations above ;

(a)State one suitable inference.

(b)State one suitable hypothesis .

(c)With the use of apparatus such as plane mirror , ray box , white paper and other apparatus, describe an experiment framework to investigate the hypothesis stated in (b).In your description, state slearly the following :

i)Aim of the experiment.

ii)Variables in the experiment.

iii)List of apparatus and materials.

iv)Arrangement of the apparatus.

v)


vi)The way you would tabulate the data.

vii)The way you would analyse the data

Refraction of a wave occurs when the wave moves from one medium to another which causes to travel at different speed.

The refraction occur when a water wave moves from deeper water to shallower water, a light wave moves from air to water , and a sound moves from air to carbon dioxide gas.

When the refraction of a wave happened , the frequency, f does not change but the wavelength ,, the speed , v and the direction of propagation of the wave change.

Refraction of water wavesThe refraction of water waves occur when the water waves move into different depth of water. Mediumv(f

Shallow waterdecreasedecreaseconstant

Deep waterincreaseincreaseconstant

If the waves meet the boundary between deep and shallow water at an angle , then the direction of the waves changes.

The plane wavefronts will change to the curved wavefronts if the waves move into the curved boundary.

To investigate the refraction of water waves a perspex plat is placed on the bottom of a ripple tank to make a shallow region of the water on the perspex plat.

The following figure shows two examples pattern of the refraction of the water waves.

(a)

(b) (c)

(d) (e)

(f)

The experiment to investigate the relationship between the depth of water and the wavelength of a water wave.Hypothesis:

The depth of water increases as the wavelength of water waves increases.


To investigate the relationship between the depth of water and the wavelength of water waves.


Manipulated variable: depth of water

Responding variable: wavelength

Constant variable: frequency

List of apparatus and materials:Ripple tank, lamp, motor ,wooden bar , power supply white paper , protractor ,plane reflector , perspex plate , metre rule and mechanical stroboscope.Arrangement of the apparatus:

The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable.The depth of water on a perspex is measured by using a metre rule = d

The power supply is switched on to produce plane waves which propagate onto the perspex plate .

The waves are freeze by a mechanical stroboscope.


The distance between 11 successive bright bands is measured by the metre rule = x

The wavelength is calculated i.e. = x 10The experiment is repeated 5 by increasing the number of perspex plate to change the depth the water.

Tabulate the data:

d

Analysis the data:

Plot the graph against d

Refraction of water wave of the sea water

When the water waves propagated from the sea to the beach , the water waves follow the shape of the beach.

It is because the water waves propagate from the deep water to the shallow water. The speed and wavelength decrease as the waves approach the beach and hence the water wave is refracted towards the normal.

The water in the bay stationary compared to the water at the cape.

It is because the depth of water varies slowly across the area of the bay and the energy of the water wave spreads to a wider area 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.

Refraction of light wavesRefraction of light waves is a phenomenon where the direction and speed of light are changed ( change in velocity) when it crosses the boundary between two materials of different optical densities

When a light waves travels from optically less dense medium to optically denser medium , the ray is bent towards the normal.

After entering the denser medium the speed of light decreases.

When a light wave travels from optically denser medium to optically less dense medium , the ray is bent away from the normal.

After entering the less dense medium the speed of light increases.

Experiment to investigate the relationship between the angle of incidence and the angle of refraction.

Hypothesis:

The angle of refraction increases as the angle of incidence increases.


To investigate the relationship between the angle of incidence and the angle of refraction.



Responding variable: Angle of refraction

Fixed variable: Refractive index

List of apparatus and materials:Glass block, ray box, white paper , protractor, power supply .



The glass block is placed on a white paper.

The outline of the sides of the glass block are traced on the white paper and labeled as ABCD.

The glass block is removed.

The normal ON is drawn.

By using a protractor , the angle of incidence is measured = i

The glass block is replaced again on its outline on the paper.

A ray of light from the ray box is directed along incidence line.

The ray emerging from the side CD is drawn as line PQ.

The glass block is removed again.

The point O and P is joined and is drawn as line OP.


Tabulate the data:

i

r

Analysis the data:


Refraction of sound waves

Refraction of sound waves occurs when the sound passes through layers of air at different densities or temperatures.

Sound waves can be refracted by a balloon filled with carbon dioxide.

When the stopwatch is started , the listener can detects at a point only beyond the balloon where the sound wave is strongest.

It is because a balloon of carbon dioxide( denser than air) acts like a convex lens ,focusing the sound wave.Effects of refraction of a sound wave at night

Distant sounds often appear louder and clearer at night.

At night the air near the ground is often cooler than the air higher up, because it is close to the cold ground. The sound waves travel faster through the warmer , less dense layers of air , and this refracts the sound wave back toward the ground.

1Which figure shows water waves travelling on the surface of the water in a ripple tank?

2When water waves pass from deep water into shallow water, how do the speed, wavelength and frequency change?

SpeedWavelengthFrequency

AIncreasesDecreasesNo change

BDecreasesIncreasesDecreases

CIncreasesIncreasesNo change

DDecreasesDecreasesNo change

3The figure shows a water waves in a ripple tank

with a sloping base.

Which of the following physical quantity

increases?

Aspeed

Bamplitude

Cfrequency

4The diagram shows a plane water waves pass from deep water into shallow water.


AThe direction of the wave propagation unchanged

BThe frequency of the waves unchanged

CThe wavelength of the waves increases

D The speed of the waves increases5Diagram shows water waves propagate in an area of different depths.

Which of the following diagrams show the propagation of the waves correctly?

6The diagram shows water waves travel from region P to region Q.


A The density of water in P greater than in Q

B The depth of water in P greater than in Q

C The speed of water waves in Q greater than in P

D The amplitude of water waves in Q greater than in P

7The figure shows a plane wave are made in a ripple tank with a sloping base to make the depth of water at X and Y is different. Which of the following shows the pattern of the wave when it reaches at P?

8The figure shows a stone is thrown by a boy in a pond with a sloping base.

Which of the following figure shows the pattern of water waves after the stone is thrown?

9The figure shows the arrangement of apparatus to shows a wave phenomenon.

Which of the following phenomenon involved?

Areflection

Brefraction

Cdiffraction

Dinterference

10A set straight water ripples in a ripple tank travels over a thick, triangular perspex sheet.

Which figure shows the wave pattern?

11Diagram shows the propagation of water waves from region X to Y.

Which is the correct comparison of the wave speed and depth of water in X and Y?

Wave speed Depth of water

AvX > vYX > Y

BvX > vYX < Y

CvX < vYX > Y

DvX < vYX

(b)Size of aperture

(c)Edge of a obstacle

(d) Small obstacle

The factors affected size of bending

(1) Size of aperture : The bigger the size of aperture the

smaller the size of bending

(2) Wavelength : The longer the wavelength , the bigger the

size of bendingThe experiment to investigate the relationship between the size of aperture and the angle of bent

Hypothesis:

The angle of bent increases as the size of aperture decreases


To investigate the relationship between the angle of bent and the size of aperture


Manipulated variable: size of aperture

Responding variable: angle of bent

Fixed variable: frequency of vibrator

List of apparatus and materials:Ripple tank, lamp, motor ,wooden bar , power supply white paper , two pieces metal bar ,metre rule protractor and mechanical stroboscope.



By using a metre rule , the width of the slit is measured = a

The power supply is switched on to produce plane waves which propagate towards the aperture.



By using a protractor , the angle of bent =

The experiment is repeated 5 times for with different widths of slit.

Tabulate the data:

a

Analysis the data:

Plot the graph against a

Diffraction of light waves

The diffraction of light waves occur when the light waves pass through a small slit or small pin hole.

Diffraction occurs at all edges where waves can spread round into the shadow region. Thus a narrow object like a fine wire or a human hair can show the diffraction fringes at its edges similar to those produced by a small single slit.

The diagram shows the diffraction fringes.

The wider middle bright fringe shows that the light

waves diffracted after pass through a small slit.

The experiment to investigate the relationship between the size of slit and the wide of the middle bright fringe

Hypothesis:

The wide of the middle bright fringe increases as the size of slit decreases


To investigate the relationship the wide of the middle bright fringe increases and the size of slit decreases


Manipulated variable: size of slit Responding variable: the wide of the middle bright fringeFixed variable: the monochromatic light (one wavelength only)


Monochromatic light source, single slit plate, metre rule



The width of the slit is recorded = a

The light beam from the source is directed towards the slit..

By using a metre rule , measure the wide of the middle bright fringe = x

The experiment is repeated 5 times for with different widths of slit.

Tabulate the data:

a

x

Analysis the data:

Plot the graph x against a

Diffraction of sound waves

Sound diffracts very readily. This is why we can hear sound round a corner , or behind an obstacle. The reason is the sound waves have long wavelengths in air, ranging from a few centimetres up to several metres. As we have already seen, long wavelength waves diffract more readily than those with short wavelengths.

To investigate the diffraction of sound waves the following experiment can be done:

A listener is requested to stand on the other side of the corner of the wall so that the radio is beyond his vision.

The listener is able to hear the sound of the radio although it is behind the wall.

It is because the sound of the radio spreads around the corner of the wall due to diffraction of sound.

1Which of the following figure is true to show the diffraction of a water wave?

2Which of the following diagrams shows the wave pattern correctly when plane waves pass through a gap?

3How do the frequency and wavelength change when waves in a ripple tank pass through a narrow gap in a barrier?

Frequency

Wavelength

Aincrease

increase

Bdecrease

decrease

Cunchanged

unchanged

4Diagram shows plane waves moving towards a slit.

The motion of the waves through the slit will cause a change in the

Aamplitude

Bwavelength

Cwave speed

Dfrequency

5Diagram shows plane water waves approaching a slit between two obstacles. The angle of increases when________________

Athe size of slit increases

Bthe frequency of the wave increases

Cthe wavelength of the wave increases

6Diagram shows a boat behind a concrete barrier.

When the sea waves approach the barrier, the boat is seen moving up and down. This is because the sea waves undergo

A reflection

B refraction

C diffraction

D interference7A driver is able to hear the sound of another car although the car beyond his vision . The phenomenon involved is

A Refraction

BInterference

C Diffraction

DReflection8The figure show a listener a student is requested to stand the other side of the corner of the wall of high building.

The student is able to hear the sound of the radio.

The phenomenon involved is

A Refraction

BInterference

C Diffraction

DReflection

9Diagram shows the waves transmitted by the

transmission station are block by the hill.

Which the following phenomenon explain that the television set in the house can still

received the transmission.

A Reflection

B Refraction

C Diffraction

D Interference

10The effect of diffraction of a light waves passes through a slit is very obvious when

A the distance between the source of light and the slit is increased

B the distance between the source of light and the slit is decreased

C the size of slit is increased

D the size of slit is decreased

11The figure shows the pattern of formed on a screen when a monochromatic light is passed through a slit. Which of the following diagram occurs when the size of the slit is decreased?

12Which of the following diagram shows the patterns of diffraction of light waves when a monochoromatic light source is passed through a small pin hole.

13Sound waves are more easily diffracted in comparison to the light waves because

Athe amplitude of sound wave is much bigger than the amplitude of light wave

Bthe frequency of sound wave is much higher than the frequency of light waves

Cthe wavelength of sound wave is much bigger than the wavelength of light waves

14Diagram 14 shows the pattern of water waves moving towards a gap between two walls at a water-theme park. Frequency of the water wave is

5 Hz.

Diagram 14 (a) (i)On Diagram 14, draw the pattern of

water waves after passing through

the gap.

(ii)Name the wave phenomenon involved

(b) Calculate the velocity of the water waves. (c) Explain how this phenomenon occurs.

..

..15Diagram 15.1 shows a plane water waves of passing through a small slit.

Diagram 15.2 shows a plane water waves passing through a small obstacle.

Diagram 15.1

Diagram 15.2

(a)Observe Diagram 15.1 and Diagram 15.2 and state two similarities of the wave patterns.

(b)Relate your answers in (a) to deduce a relevant physics concept and name the concept.

16Diagram 16 shows the positions of two policemen A and B standing behind the two tall buildings. The policemen are holding a walkie-talkie each. The two buildings are 4 m apart.

Diagram 16

(a)Radio waves are a type of

..waves

(b)(i)Name the wave phenomenon which

enables the policemen to communicate with each other.

............................................................

(ii)Name two factors that affect the

effectiveness of the above phenomenon.

...................................................................

................................................................... Table 16 shows a few radio frequencies suggested by the policemen.

Suggested frequencies

50 MHz

500 MHz

5 GHz

Table 16(c)Calculate the wavelengths of each of the radio waves suggested by assuming the speed of radio waves in air is 3.0 x 108 ms1.

3.0 x 108 = (50000000 )() = 6 m 3.0 x 108 = (500000000)()

= 0.6 m x 108 = (5000000000()

= 0.06

(d)Based on your answer in (c), which is the most suitable radio frequency to be used by the policemen. Explain your answer.

.......................................................................

.......................................................................

17Diagram 17.1 shows a water waves passing through a

log that floats in water. Diagram 17.2 shows a student standing at one corner

of a building at B who can hear the sound from a

loudspeaker at A.

Diagram 17.1 Diagram 17.2

(a)Based on Diagram 17.1 and Diagram 17.2,

(i)what happens to the wave after passing round the log and the corner of the building?

(ii)what happens to the amplitude of the waves after passing round the log and the corner of the building? Explain your answer.

...

(iii)name the wave phenomenon that is related to Diagram 17.1 and Diagram 17.2.

(iv)what will happen to the speed of the water waves after passing through the log?

...

(b)Referring to Diagram 17.1, what will happen to a floating object that is placed at

(i)P .....................................

(ii)Q......................................

(c)Name one other wave phenomenon that occurs in Diagram 17.1.

18The figure shows the bright and dark bands of the wave patterns formed on the screen when plane waves pass through narrow and wide slits. Observe the figure. Compare the wave patterns and the wavelengths of the waves before and after they pass through the slits.

Relate the size of slits, the wave patterns and the wavelengths to deduce a relevant physics concept.

Name the wave phenomenon shown in the figure.

19 To attract more tourist to the island in Diagram 19, a contractor wants to build a beach resort

Diagram 19.As a consultant you are asked to give suggestions on the proposed project based on the following aspects:

-The location of the resort

-Features to reduce the erosion of the shore

-Features to enable children to enjoy swimming in calm water.20

Diagram 20Diagram 20 shows the sea water waves passing through two different gates at a harbour .

Based on the observations:

(a)State one suitable inference that can be made.

(b)State one appropriate hypothesis for an

investigation

(c) With the use of apparatus such as ripple

tank, stroboscope and other apparatus, describe

an experimental framework to test your

hypothesis.

In your description, state clearly the following:




(iv)Arrangement of the apparatus

(v)The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable


(vii) Way you would analysis the data

Meaning of Interference

Interference is the superposition of two waves originating from two coherent sources.Two waves are in coherent if they are of the same frequency, same amplitude and in phase (same phase)There are two types of interference :

(a) Constructive interference occurs when the crests or troughs of both waves coincide to produce a wave with maximum amplitude.

(b) Destructive interference occurs when the crests of one wave coincide with the trough of the other waves to produce a wave with zero amplitude.

Interference of the waves is a result or obeys the principle of superposition.

Principle of superposition

Principle of superposition state that When two waves move simultaneously and coincide at a point the sum of the displacements at that point is equal to the sum of the displacements of the individual waves by vector method.

(a) Superposition of two crests

Constructive interference

Antinode is a point at which

constructive interference occurs.

(b) Superposition of two troughs

Constructive interference

Antinode is a point at which

constructive interference occurs.(c) Superposition of a crest and a trough

Destructive interference

Node is a point at which

destructive interference occurs.

...interference occurs

Interference of water waves

To produce the interference pattern of the water waves in a ripple tank we can use:

(a)Two dippers operated from the same motor,

Or

(b)A plane water waves passing through two slits.

Analysing Interference pattern of water waves

The figure shows the interference pattern produced by two sources of water P and Q.

To analyse the interference pattern of water waves ,please follow this instructions:

1.Mark with a cross (x) in the figure the points where the crests coincide crests .

2.Mark with a star (*) in the figure the points where the troughs coincide troughs .

The points (x) and (*) is called as _____________.

_______________ is a point where the total

displacement is ______________or ____________.

At the points ______________interference occurs.

3.Mark with a circle () in the figure the points where a crest coincide with a trough.

The points () is called as _____________.

_______________ is a point where the total

displacement is ______________.

At the points ______________ interference occurs.

4.Connect the points (x) and (*) to produce several lines that we call as _____________________ lines

5.Connect the points () to produce several lines that we call as _____________________ lines

6.Draw a straight line parallel to sources. We can the line as ____________________line

7.Measure the distance between the two sources, a = ................................ cm

8.Measure the distance between the sources and the detector line,D =................................cm.

9.Measure the distance between two successive node lines, x =................................cm

10.Calculate the value of a x = .................cm

D

11.Measure the wavelength of the water waves, (

=..............................

12.Compare the value of ( with a x

D

Hence ( = a x

D

Where , = the wavelength of the water

waves a = the distance between two

dippers x = the distance between two

successive nodal or

antinodal line

D = the distance between dippers

and detector lineHow to change the pattern of interference of waves?

The pattern of interference depends on the distances between two consecutive nodal or antinodal lines , x.

How to change x ?

From the formula = a x D

Hence x = D a

Conclusion : As increases , x increases

As D increases , x increases

As a increases , x decreases

As increases , x increases

As a increases , x decrease

The experiment to investigate the relationship between the distance between to coherent sources and the distance between two consecutive nodal lines

Hypothesis:

The distance between two consecutive node lines

increases as the distance between to coherent sources decreases


To investigate the relationship between the distance between to coherent sources and the distance between two consecutive node linesVariables in the experiment:

Manipulated variable: the distance between to coherent sources Responding variable: the distance between two consecutive node linesFixed variable: frequency of vibrator or the wavelength

List of apparatus and materials:Ripple tank, lamp, motor ,wooden bar , power supply ,white paper , spherical dippers ,metre rule and mechanical stroboscope.



By using a metre rule , the distance between two dippers is measured = a

The power supply is switched on to produce two circular waves from the dippers



By using the metre rule , the distance between two consecutive nodal lines is measured = xThe experiment is repeated 5 times for with different distances between two dippers

Tabulate the data:

a

x

Analysis the data:

Plot the graph x against a

Example 1

In an experiment to investigate the pattern interference of a water waves, the distance between two spherical dippers is 2.5 cm and the distance between two consecutive antinodal lines is 5.0 cm. What is the wavelength of the water waves if when the distance from two dippers to the point of measurement is 10 cm.

Solution

Interference of light waves

When light from the same source passes through two

narrow slits which are close together the effect

known as interference can be seen as the bright and

dark fringes.

The bright fringes to be formed by constructive

Interference and the dark fringes to be formed by

destructive interference.

Interference fringes produce by using Double-slit

interference Youngs experiment.

For all practical purposes, monochromatic light is

used.

Monochromatic light which is light of only one colour

or one wavelength.

The formula for interference of light waves is,

Where,

= wavelength of light waves

a = slit separation

x = distance between two successive bright or

dark fringes

D = distance between double slit and screen.

Example 2

In a double-slit interference experiment with blue light the distance between the screen and double slit is 1.2 m and slit separation is 2 x 10-4 m . Six successive bright fringes at a distance 1.2 x 10 -2 m is formed on the screen. Calculate the wavelength of the blue light.

Solution

The experiment to investigate the relationship between the wavelength of the light waves distance and the distance between two consecutive bright fringes

Hypothesis:

The distance between two consecutive bright fringes

increases as the wavelength of light waves increases.Aim of the experiment :

To investigate the relationship between the wavelength of the light waves distance and the distance between two consecutive bright fringes


Manipulated variable: The wavelength of the light waves( colour of light)Responding variable: the distance between two consecutive bright fringesConstant variable: slit separation and the distance between double slit and screen.

List of apparatus and materials:Source of light,colour filter, screen, single slit, double slit and metre rule.



A green filter is placed between the light source and the slits.

The source of light is switched on.

The interference pattern formed on the screen is observed and drawn.

By using a metre rule the distance across 6 consecutive bright fringes is measured.

The distance between two consecutive bright fringes is calculated , x = L 5

The experiment is repeated 5 times for with different colour filters

Tabulate the data:

x

Analysis the data:

Plot the graph x against

The arrangement of colour of light in order of wavelength

Interference of sound waves

Like other types of waves ,sound waves can also give interference effects. Interference of sound waves produce regions of louder sound by constructive interference and regions quiet by destructive interference.

When two similar loudspeakers are connected to the same audio-frequency generator they will produce interference effects.

The formula for interference of sound waves is,

Where,

= wavelength of sound waves

a = distance between two loudspeakers

x = distance between two successive loud

regions or quiet region.

D = distance between the listener from the

loudspeaker.

Example 3In an experiment on the interference of sound wave a listener at distance 5.0 from the loudspeaker. The distance between two loudspeakers is 2.0 m. The loudspeakers are connected to an audio-frequency generator to produce sound waves at a frequency of 0.8 kHz.

Calculate

(a)the wavelength of sound waves when the speed of sound is 320 ms-1(b)the distance between two successive loud regions

Solution:

The experiment to investigate the relationship between distance of the listener from the loudspeaker and the distance between two successive loud regions

Hypothesis:

the distance between two successive loud regions increases as distance between the listener from the loudspeaker increases .Aim of the experiment :

To investigate the relationship between distance between the listener from the loudspeaker and the distance between two successive loud regions


Manipulated variable: Responding variable: distance between the listener from the loudspeaker

Responding variable: the distance between two successive loud regions

Constant variable: the wavelength of sound waves , distance between two loudspeakersList of apparatus and materials:Two loudspeakers, audio-frequency generator ,connection wires and metre rule.



By using a metre rule the distance between the listener from the loudspeaker is measured= D

The audio-frequency generator is switched on.

The listener is requested to walk in a straight path and the distance between two successive loud regions is measured by a metre rule = x

The experiment is repeated 5 times for with different distances between the listener from the loudspeaker Tabulate the data:

D

x

Analysis the data:

Plot the graph x against D

1The figure shows two impulse waves traveling towards each other along the length of a rope.

Which of the following figure shows the pattern of the impulse waves after passed through point O.

Which of the following figure shows the pattern of the impulse waves after passed through point O.

2Figure shows two impulse waves travelling towards each other.

Which of the following figure shows when both waves meet at the point P?

3The figure shows two impulse waves travelling towards each other with a speed 2 cms-1 respectively.

Which of the following shows the pattern of the impulse waves after 1 s?

4The figure shows an interference pattern of two coherent water waves of sources, P and Q.

Which of the positions A,B,C or D, does the amplitude of the water waves is zero.

5The figure shows the wave pattern formed by waves from two coherent sources.

Antinode points are

AW and X

BX and Z

CY and Z

DW and Y

6The figure shows plane water waves approaching two slits between three obstacles.

The phenomena involved are

Arefraction and reflection

Breflection and diffraction

Crefraction and interference

Ddiffraction and interference

7Monochromatic light which is light of only one ____

A phase

B colour

C amplitude

D intensity

8The figure shows a monochromatic light is passed through a double slit.

Which of the following formed on the screen?

A two bright bands

B a spectrum of light

C a pattern of alternating bright and dark regions

9The figure shows the fringe pattern obtained in a double slit experiment when a monochromatic light is used. The slits are 3 x 10-4 m apart and the screen is 3.0 m away from the slits.

What is the length of the monochromatic light ?

A5x10-7 m

C 2.5 x10-6 mC 7.5x10-6 m

D 5 x 10 - 8 m

10In an experiment of light interference using green light of wavelength 5 x 10 - 7 m , two consecutive bright fringes formed on the screen are 0.4 mm apart.

When the experiment is repeated using red light two consecutive bright fringes formed 0.48 mm are apart.

What is the wavelength of the red light ?

A 2.4 x 10 - 7 m

B 4.2 x 10 - 7 m

C 5.0 x 10 - 7 m

D 6.0 x 10 - 7 m

11In an experiment of light interference , the distance two successive bright or dark fringes depends on

Awidth of slit

Bcolour of light is used

Cintensity of the source of light is used

12The figure shows the arrangement of apparatus in Youngs double slit experiment.

The distance between two consecutive bright fringes increases whenAslit separation increasesBthe width of slit increases C the distance between the screen and the double-slit plat decreases

D the green filter is replaced by a red filter.

13The figure shows are the patterns of interference by using red filter, green filter and blue filter which are not arranged in order.

Which of the following is the correct filter for respective patterns of interference?

P

Q

R

A red

blue

green

Bblue

red

green

Cgreen

blue

red

Dgreen

red

blue14In an experiment of light interference the distance between two consecutive bright fringes ,x varies with distance between double slit and screen, D.

Which of the following graphs shows the correct relationship between x and D?

15In experiment of the interference of waves, two loudspeakers are placed at a distance of 1.5 m from each other. The distance between two consecutive soft sounds is 6.0 m and the listener at a distance 4.5 m from the loudspeakers.

What is the wavelength of the sound waves is used?

A1.25 m

B1.50 m

C 2.00 m

D3.00 m

16The figure shows the arrangement of apparatus the interference of sound waves experiment.

The distance between two consecutive loud sounds increases as

Athe diameter of the loudspeaker increases

Bthe frequency of the audio-frequency generator increases

Cthe distance between two loudspeakers increases

Dthe distance between the loudspeaker and the line XY increases

17Diagram 17 shows an experiment to determine the wavelength of monochromatic light waves by using a red light source.

Diagram 17

(a)What is meant by monochromatic light?

....

(b)Why are red fringes formed on the screen ?

............................................................................

(c)The distance between the Young double slit and the screen is 3.0 m. The double slit used has the slit separation is 5 x 10-4 m.

Calculate the wave length of the red light.

(d)The red light is replaced by the green light.

(i)What happen to distance between two consecutive dark fringes.

(ii)Give the reason for your answer in (d)(i).

(d)(i).

............................................................................

............................................................................

18Diagram 18.1 and Diagram 18.2 show fringes are formed when identical monochromatic lights pass through the double slits.

Diagram 18.1 Diagram 18.2(a)What is the meaning of monochromatic light?

........(b)Explain how fringes are formed on the screen?

..............(c)Using Diagram 18.1 and Diagram 18.2 ,compare(i)the distance between the slits, a.

(ii)the wavelength of the light, , that passes through the double slits....(iii) the distance between the double slits and the screen, D.

...(iv)the distance between the fringes, x.

...

(d)Using your answers in 6 (c) state the

relationship between x and a .

19Diagram 19.1 shows two identical loudspeakers, L and M connected to an audio signal generator which produces a note of constant frequency.

Diagram 19.1

(a)(i)Name the phenomenon shown in

Diagram 19.1.

...............

(ii) The loud sound is heard by the observer at

P. Explain what happens at point P.

..

(b)Given that the frequency of the audio signal generator is 2000 Hz and the velocity of sound in air is 340 m s-1.

Calculate the wavelength of the sound wave.

(c) The observer then walks slowly along ST. He hears loud sound and weak sound alternately. Diagram 19.2 shows the positions of the loud and weak sounds.

Diagram 19.2

State how to decrease the distance between two points where loud sounds are heard in terms of the distance between two loud speakers and the frequency of the audio signal generator.

Explain your answer.

(i)the distance between two loud speaker

.

Explanation :

...

(ii) the frequency of the audio signal generator

.

Explanation :

...

(d)Diagram 19.3 shows a headphone which is used by an air traffic officer at the airport to reduce incoming loud noise. The incoming noise is detected by the microphone and is processed by a system of a computer and speakers inside the headphones.

Diagranm 19.3

(i)State the phenomenon that is used to reduce the noise by the computer and the microphone in the headphone.

...(ii) Draw a wave form diagram to explain your answer in 7(d) (i).

20A student carries out an experiment to investigate the interference of sound waves. Two loudspeakers are connected to an audio signal generator. The student measured the distance between two adjacent loud sounds, x, for different values of frequency, f. The student then plots a graph of f against as shown in Diagram 20 Diagram 20(a)Based on the graph on Diagram 20,

(i)State the relationship between x and f.

..

(ii)Determine the frequency, f, when the distance between two adjacent loud sounds, x, is 2.0 m. Show on the graph how you determined f.

(iii)Calculate the gradient of the graph, m.

Show on the graph how you determined the gradient.

(b)Given that and v = f(, write an expression of v in terms of D, f, a,v and x.

(c)Given that x f = m.

By using the value of the gradient, m, obtained in (a)(iii) and the expression in (b), calculate the velocity of sound in air when D = 2.8 m and a = 1.2 m.

(d)State two precautions that should be taken during this experiment.

....

21 Diagrams 21.1 and 21.2 show interference patterns

using coherent sources of waves, .

Diagram 21.1

Diagram 21.2

(a) What is meant by coherent waves ?

(b) Compare Diagram 21.1 and 21.2 .

Relate and x to make a deduction regarding the

relationship of both quantities.

22A student who moves his ear near a vibrating tuning

fork hears loud and soft sounds alternately.

Diagram 22.1 shows the positions of loud sounds are

closer together.

Diagram 22.2 shows the positions of loud sound are further apart.

Diagram 22.1 Diagram 22.2

Based on the information and observation:

(a)State one suitable inference.

[1 mark]

(b) State one suitable hypothesis. [1 mark]

(c) With the use of apparatus such as two loudspeakers, signal generator and other apparatus, describe one experiment to investigate the hypothesis stated in (b) In your description, state clearly the following:




(iv)Arrangement of the apparatus

(v)The procedure of the experiment which include the method of controlling the manipulated variable and the method of measuring the responding variable


(vii) Way you would analysis the data

Producing sounds

Sound waves are longitudinal waves that are transmitted through almost any substance i.e solid , liquid or gas.

The waves are produced by any mechanism which produces compressional vibrations of the

surrounding medium. Some examples are the vibrating string of a guitar, exploding gas in firecracker and the vibrating diaphragm of a loudspeaker.

Vibrations in a vacuum

Sound cannot travel through a vacuum because in a vacuum there is no material to transmit the compressions. A common demonstration of this to show that is a ringing bell cannot be heard if the bell is in a vacuum chamber. The bell is vibrating , but there is no surrounding material to carry the vibration to our ears.

Similarly we cannot hear the nuclear explosions on the sun because there is no medium in space. Astronauts cannot speak to each other on the moon without using radio waves, because there is no air on the moon through which sound waves can travel.

Sound waves in air

Sound waves are longitudinal waves. The sound waves from a loudspeaker produce compressions and rarefactions of the air molecules. When molecules pushed forwards (to the right) meet molecules bouncing backwards(to the left) , after collisions with other molecules in front, a region of compression is produced where the air pressure is higher. In between the compressions are rarefactions where the number of molecules is reduced and air pressure is lower.

Thus we may describe a progressive wave sound in air as a travelling pressure wave in which regions of increased air pressure travel along where the air molecules are compressed together separated by regions of reduced air pressure at the rarefactions.

Speed of sound

Sounds travels quickly, but not nearly as fast as light. The speed of sound waves depends on the medium. Sound travels fastest in solids, and slowest in gases.

Sound travels more quickly through medium in which the atoms are strongly bound together. If you imagine that in a solid all the atoms are joined together by springs then the stronger the springs the faster the sound travels. The strong binding between atoms in solids means that sound will travel much more quickly through solids than through gases.

The speed of sound waves in gases increase when the density of the gases decrease. When the density of the gases decrease ,the frequency of the vibrations increase ,so the speed of the sounds increase ( v = f)

The speed of the sound waves also increase as the temperature the gases increase. It is because when the temperature of the gases increase the density of the gases decrease.

The speed of sound waves in a gas not affected by changes of pressure.

Typical values for speed of sound are given in the following table.

MediumSpeed of sound waves/ ms-1

Air (0oC)331

Oxygen (0oC)316

Helium (0oC)965

Hydrogen (0oC)1284

Water (0oC)1402

Water (20oC)1482

Water (50oC)1543

Aluminium (0oC)5100

Copper (0oC)3560

Iron (0oC)5130

The frequency spectrum of sound wavesIf a signal generator is connected to a loudspeaker , not all the frequencies of the sound wave is produced ca be heard by the human hear.

The human hear is capable of hearing sounds with frequencies in the range of 20 Hz to 20 000 Hz.

The following figure shows the frequency spectrum of sound waves:

Below about 20 Hz the vibrations are felt rather than heard e.g. earth quakes and are called subsonic.

We are able to hear sounds with frequencies from around 20 Hz to almost 20 000Hz.

Sounds above the upper hearing limit are called ultrasound.

Dogs, bats and dolphins are all known to be able to hear sounds whose frequency is well above the limits of human hearing.

Loudness and Pitch of soundThe loudness of a sound depends on the amplitude of vibrations. As the amplitude of vibrations increase, the loudness of a sound increases.

The pitch of a sound depends on the frequency of vibrations. As the frequency of vibrations increase , the pitch of a sound increases.

Quality or timbre of sound

The quality of sound depends on the wave form.

Different musical instruments of the same pitch are distinguished from each other by their quality.

Sound and Noise

Our ear can also tell the difference between musical sounds and noises. The waveforms produced by musical instruments are regular, whilst those produced by noises are jagged and irregular.

Application of Sound WavesMedicine

(1)Ultrasonic scanning in medicine involves sending ultrasound waves into the patients body and detecting the echoes which come back. This can be used , for example, to see the position of an unborn baby inside its mothers womb. The whole process is completely painless and much safer than using X-rays.

(2)Sound waves of high energy are directed to the kidney stones to destroy them in the cavity of the kidney. The disintegrated particles are removed during urination by the patient.

(3)Dentist use ultrasonic waves to remove plaque from the teeth.

(4)Ultrasound spectacles help blind persons to estimate the distance away of something in front of them.

Industry

(1)Ultrasonic scanning is used to detect cracks in metal structures . This is how aircrafts parts are checked for hidden cracks which might prove dangerous later.

(2)A goldsmith uses high frequency sound waves to dislodge dirt particles adhering to jewellery and precious stones.

(3)Ships use echo-sounding equipment to find how deep the water is. The time interval is measured between a pulse of sound and its echo from the sea bed.

If the echo-sounders measures an interval of time ,t , and the speed of sound wave in water is v, the depth , d can be calculated as follows;

Distanced travelled by pulsed = speed x time

2d= v x t

(4) In modern fishing trawlers, echo -sounding

Produces SONAR ( Sound Navigation and Ranging) is used to detect shoals of fish. The equipment can detec

chapter 6 2010- waves

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