Chp 1 waves by HAN GUAN NG

Mr Ng Han Guan Guru Cemerlang Physics MSAB

Form 5 Chapter 1: Wave Date:

CHAPTER 1: WAVE 1.1

UNDERSTANDING WAVES

A wave is a kind of vibration or oscillation that allows energy transfer from one point to another without transferring matter.

Waves can be produced by a system that vibrates or oscillates.

Examples of waves: 

Light waves



Sound waves



Water waves

Propagation (travelling) of wave is the transfers of energy and the momentum from the source of the wave to the surroundings. 

As the sound waves come out of the speaker, we can see that the flame flutters.



This shows that energy of the sound waves can be transferred from the speaker to the candle.

1.1.1 1.

Wavefront A wavefront is an imaginary line or surface that connects all vibrating particles that are in the same phase (in phase).

Points in a wave are in phase if they vibrate in the same direction with the same displacement.

Particles in the same wavefront have the same speed and are at equal distances from their source.

There are two types of wavefront: 

Circular wavefronts



Plane wavefronts.

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.1.2

Form 5 Chapter 1: Wave Date:

Types of waves  Transverse wave

There are 2 types of waves:

 Longitudinal wave

1. Transverse wave  The direction of propagation of wave is perpendicular to the direction of vibration of particles.  The wavelength,  is the distance between two successive crests or troughs. A

A = crests B = troughs B

 Example of transverse wave: i.

Water wave

ii. Light wave

iii. Electromagnetic wave

2. Longitudinal waves  The direction of propagation of wave is parallel to the direction of vibration of particles.  The wavelength,  is the distance between two successive compressions or rarefactions. P

P = compressions Q = rarefactions Q

 Example of longitudinal wave: Sound wave

1.1.3 Properties of a Waves Motion Properties

Definition

Equilibrium position

The position of the object where is no resultant force acts on the object

Amplitude, A

The maximum displacement from its equilibrium position

Crest (or Peak)

The highest point reached by a vibrating particle in a transverse wave.

Trough

The lowest point reached by a vibrating particle in a transverse wave.

Period, T

Frequency, f

The time taken by one oscillation (one complete oscillation or wave). The S.I. unit is second (s). T = 1/f The number of complete oscillations produced in one second. The S.I. unit is Hertz (Hz). f = 1/T The distance moved by a wave in one second. The SI unit of velocity is metre

Wave speed, v

In Phase

per second (m s-1). v = f  =

 T

f=

1 T

When the particles of wave are moving in the same direction with the same speed and have the same  displacement from the rest position.



Mr Ng Han Guan Guru Cemerlang Physics MSAB

Form 5 Chapter 1: Wave Date:

1.1.4 Graph for a Wave

Displacement – time graph

1.1.5

Displacement – distance graph

Damping

1. In an ideal condition, there is no energy gained or loss in an oscillation system. 2. But in a real situation, there is some loss of energy due to friction, air resistance or other nonconservative force. As the energy of a system decreases, its oscillation decreases as well. 3. Damping is a process where the amplitude of an oscillating system decreases slowly until the system stops oscillating. 4. Damping is usually caused by (type): i.

External damping  loss of energy due to overcome external frictional forces such as air resistance.

ii. Internal damping  loss of energy due to the extension and compression of the molecules in the system. Only amplitude, and energy of the system decrease but frequency, does not change.

1.1.6

Resonance

1. The external force supplies energy to the system to enable an oscillating system to go on continuously  Forced Oscillation 2. The frequency of a system that oscillates freely without the action of an external force is called the natural frequency. 3. A resonance is the phenomenon when the oscilating system is driven (force) to oscillate at its natural frequency by an external force. System oscillates at its maximum amplitude. 3 3rd edition © 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan

Mr Ng Han Guan Guru Cemerlang Physics MSAB

Form 5 Chapter 1: Wave Date:

Experiment to show a phenomenon of resonance  Barton’s pendulum

1. The natural frequency of a simple pendulum depends on its length. 2. When pendulum X is set into oscillation, its energy is transferred through a thread to another pendulum. Other pendulums are forced to swing at the same frequency as X. 3. But pendulum X and D have the same length, so there have same natural frequency. So pendulum D will oscillates with maximum amplitude. 4. The effects of resonance: i.

Constructive (useful)  Electrical resonance: The reception of radio programmes from a distant transmitting station.  Molecular resonance: The cooking of food using the microwave oven.  Mechanical resonance: The production of sound in many musical instruments.

ii. Destructive (damage)  A bridge can collapse when the amplitude of its vibration increases as a result of resonance  Tacoma Narrows Bridge at Puget Sound, Washington in 1940.  In an earthquake, buildings often vibrate in resonation to seismic waves causing them to collapse.

1.2

ANALYSING REFLECTION OF WAVES

1. Reflection of a wave occurs when a wave strikes an obstacle such as barrier, plane reflector, mirror and wall. 2. The reflection of waves obeys the law of reflection: i.

The angle of incidence, i is equal to the angle of reflection, r.

ii. The incident wave, the reflected wave and the normal all lie in the same plane. Properties Of Water Waves

After Reflection

Wavelength, 

Unchanged

Frequency, f

Unchanged

Speed, v

Unchanged

Velocity, v

Changed

Direction of propagation of wave

Changed according to the angle of incidence

3. Plane waves reflected by a concave barrier will converge to a focus. 4. Plane waves reflected by a convex barrier will diverge. 4 3rd edition © 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.2.1

Form 5 Chapter 1: Wave Date:

Pattern of Reflected water waves

Reflection of Light Wave

Reflection of sound waves

 The angle of incidence, i is equal to the angle of reflection, r.  The Laws of Reflection is obeyed.

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.2.2

Form 5 Chapter 1: Wave Date:

Applications of Reflection of Waves in Daily Life

1. Safety: The rear view mirror and side mirror in a car. The mirrors reflect light waves from other cars and objects into the driver’s eyes. 2. Defence: A periscope use in the submarine. The light waves from an object that is incident on a plane mirror in the periscope are reflected twice before entering the eyes of the observer. 3. Telecommunications: Infrared waves from the remote control of electrical equipment are reflected by objects in the surroundings and received by the television set or radio. Working Principle of a Ripple Tank

1.3

ANALYSING REFRACTION OF WAVES

The refraction of waves occurs when there is a change of direction of the propagation of waves travelling from a medium to another medium due to a change of speed. Properties Of Refracted

Deep Water to

Shallow Water to

Water Waves

Shallow Water

Deep Water

Wavelength, 

Decreases

Increases

Velocity, v

Decreases

Increases

Frequency, f

v  f  f 

Unchanged



 constant



1



2

Direction of propagation

Bends towards

Bends away from

of wave

the normal



Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.3.1

Form 5 Chapter 1: Wave Date:

Refraction of Plane Water Waves

1. When the water wave travel from a deep area into shallow area, the direction of propagation of the waves is refracted towards the normal. 2. The angle of incidence, i of the water is greater than the angle of refraction, r. (a)

(b)

Deep

Shallow

Deep

(c)

Deep

Shallow

Deep

(d)

Deep

Shallow

Deep

(e)

Deep

Shallow

Deep

Shallow

Deep

(f)

Deep

Shallow

Deep

7 3rd edition ÂŠ 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.3.2

Form 5 Chapter 1: Wave Date:

Refraction of Light Waves

Normal

1. When a ray propagates from one medium to an optically

Air

denser medium, the ray refracts towards the normal.

Glass block

2. The speed of light decreases as it propagates in the glass block (optically denser medium), causing it to alter the direction of propagation. 1.3.3 Refraction of Sound Waves

1. On a hot day, the hot surface of the Earth causes the layer of air near the surface to be warmer. This causes sound waves to be refracted away from the Earth. 2. On a cool night, the sound waves travel slower in the cooler layer of air near the surface of the Earth than in the upper, warmer air. The waves are refracted towards the Earth. 3. Hence, sound can be heard over a longer distance on a cold night compared with a hot day. 4. A sound wave is refracted towards the normal when the wave passes from the air (less dense) to the carbon dioxide (denser) in the balloon. The balloon acts as a convex lens that converge the sound waves to the microphone. 5. If the balloon is filled with a less dense gas such as nitrogen or helium, the sound wave will be refracted away from the normal when it passes from the air to the balloon. The balloon will act as a concave lens in this case. Temperature of Air

Speed of Sound Wave

Density of Gas

Density of Medium

Hot

Cold

Less Dense

Denser

Less Dense

Denser

Faster

Slower

Faster

Slower

Faster

Refraction of Sound Wave Towards the normal

Hot to Cold

Less Dense to Denser

Denser to Less Dense

Away from the normal

Cold to Hot

Denser to Less Dense

Less Dense to Denser

Sound travels slower through denser gas because it particleâ&#x20AC;&#x2122;s mass is greater and inertia is greater. Sound travels fastest through denser medium because the molecules are more tightly linked. 8 3rd edition ÂŠ 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.4

Form 5 Chapter 1: Wave Date:

ANALYSING DIFFRACTION OF WAVES

1. Diffraction of waves is a phenomenon in which waves spread out when they pass through a gap or round a small obstacle. 2. The effect of diffraction is obvious (clearly seen) only if i.

The size of the aperture (gap) or obstacle is small enough.

ii. The wavelength is large enough (*the frequency is low).

1.4.1

Properties Of Water Waves

After Diffracted

Wavelength, 

Unchanged

Frequency, f

Unchanged

Speed, v

Unchanged

The direction of propagation

changed

the pattern of the waves

changed

Diffraction of Water Waves (b) Wider gap > λ

(a) Narrow gap ≤ λ (c) Narrow obstacle ≤ λ

(d) Wider obstacle > λ

When water waves travel through a small gap, its energy is dispersed through a larger area. Hence, the diffracted waves will vibrate with smaller amplitude.

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.4.2

Form 5 Chapter 1: Wave Date:

Diffraction of light waves

1. Diffraction of light waves is barely noticeable because light has very short wavelength. 2. Light waves will be diffracted if: (i) Light is propagated through a small slit or small pinhole (size is similar to that of the light wavelength). (ii) The light source is monochromatic  light of one colour and therefore of one wavelength only. 3. The wider middle bright fringe shows that the light waves diffracted after pass through a narrow slit. 4. If the slit becomes wider, diffraction pattern becomes less distinct.

1.4.3

Diffraction of sound waves

1. A listener is able to hear the sound of the radio although it is behind the wall (beyond his vision). 2. It is because the sound of the radio spreads around the corner of the wall due to diffraction of sound. Sound waves are more easily diffracted in comparison to light waves because the wavelength of sound waves is much longer than the wavelength of light waves.

1.5 ANALYSING INTERFERENCE WAVE

Interference is the superposition of two waves from two coherent sources meet.

Two waves are in coherent if they are of the same frequency, amplitude and are in phase.

There are two types of interference: i.

Constructive interference  Produce maximum resultant amplitude.

ii. Destructive interference  Produce zero resultant amplitude.

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.5.1

Form 5 Chapter 1: Wave Date:

Principle of Superposition

1. The principle of superposition states that when two waves overlap, the resultant displacement is equal to the sum of the displacements of the individual wave.

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

Before superposition

During superposition

Before superposition

During superposition

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

Before superposition

1.5.2

During superposition

Interference of Water Waves

1. Antinodal lines are lines joining antinodes, and antinodes are points where constructive interference occurs. 2. Nodal lines are lines joining nodes, and nodes are points where destructive interference occurs. 3. Relationship between , a, x and D   

ax D

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.5.3

Form 5 Chapter 1: Wave Date:

Interference of Light Waves

1. Same as water waves and sound waves also requires two coherent sources. 2. Two coherent light sources can produce with experiment, which is known as Young’s doubleslit experiment. 3. A ray of light passes through the single slit and reaches the double-slit will give rise to two coherent light rays. 4. The superposition of these two rays produces constructive and destructive interference. 5. The formula,  

ax to determine wavelength of light waves. Where x is the distance between D

two consecutive fringes (bright or dark). If the distance across 11 consecutive bright fringes is measured  that is, 10x.



L 11 consecutive bright fringes = L = 10 x

1.5.4



x = L / 10

Interference of Sound Waves

1. Coherent sound waves interfere with each other to produce areas of louder sound (constructive interference) and softer sound (destructive interference). 2. The formula,  

ax where x is the distance between two consecutive positions where a loud D

sound or soft sound is heard.



Mr Ng Han Guan Guru Cemerlang Physics MSAB

Form 5 Chapter 1: Wave Date:

1.6 ANALYSING SOUND WAVES

1. Sound waves are longitudinal waves, which require a medium for its propagation. 2. Sound propagates in the form of compressions and rarefactions of air. 3. The wavelength of a sound wave is the distance between two consecutive compressions or rarefactions of air molecules. 4. Bell-jar experiment can shows that sound waves cannot pass through vacuum. 5. Sound travels fastest through solid and slowest through gas. This is because the molecules in a solid are more tightly linked.

1.6.1

Properties of sound

1. The loudness of the sound is depends on the amplitude of the wave.

The pitch of the sound is depends on the frequency of the wave.

3. The quality of the sound is depends on the waveforms produced.

13 3rd edition ÂŠ 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.6.2

Form 5 Chapter 1: Wave Date:

Application of Sound Waves

1. Ultrasonic waves with frequencies above 20 kHz cannot be heard by human ear. 2. Dolphins use ultrasound frequencies of about 150 kHz to communicate with each other, to navigate and to find food. 3. An ultrasound beam is used in ultrasonic spectacles for blind people to know that whether the object causing the echo is near or far away. 4. Echo is also used to detect flaws inside pieces of metal. 5. Doctors use ultrasound to obtain a picture called a sonogram to see an unborn baby. In order to see fine details, the wavelength of the sound waves must be short. 6. Sonar (Sound Navigation and Ranging) is used to determine the depth of water and also used to detect underwater objects by means of an echo. 7. The depth of sea water can be calculated using the formula:

1.7 ANALYSING ELECTROMAGNETIC WAVES

d=vx

t 2



The electric and magnetic field vibrate perpendicular to each other and to the direction of propagation.

1.7.1

Properties of electromagnetic waves



Transverse waves



Do not require a medium to propagate and can travel in a vacuum



The waves travel at the speed of light, c = f = 3 x 108 m s-1 through a vacuum



Undergo the same waves phenomenon : reflection, refraction, diffraction and interference



Have different frequencies and different wavelengths



Unaffected by external electric and magnetic fields 14

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.7.2 

Form 5 Chapter 1: Wave Date:

Electromagnetic Spectrum The range of frequencies and wavelengths over which electromagnetic waves are propagated.

Type of electromagnetic wave Radio waves  = 10-1 ~ 105 m

Source

Application

Electrical oscillating circuit (SW, MW, LW, VHF, UHF)

Microwave  = 10-3 ~ 10-1 m

Special electronic devices such as the klystron tube

Infrared  = 10-6 ~ 10-3 m

Hot bodies, the sun and fires

Visible light  = 10-7 m

The sun, hot objects, light bulbs, fluorescent tubes

Ultraviolet radiation  = 10-9 ~ 10-7 m

Very hot objects, the sun, mercury vapour lamps

X-ray  = 10-11 ~ 10-9 m

x-ray tubes

Gamma rays  = 10-14 ~ 10-10 m

Radioactive substances

1.7.3

 Television transmission  Telecommunications  Communications in radio, airplanes and ships - Mobile phone networks - Radar systems - Satellite transmissions - Night vision - Thermal imaging and physiotherapy - Remote controls for TV - Sight - Photosynthesis in plants - Photography - Identification of counterfeit notes - Production of vitamin - Sterilisation to destroy germs - Radiotherapy - Detection of cracks in building structures - Can show the condition of a person’s bones - Cancer treatment - Sterilisation of equipment - Pest control in agriculture

Effects of Electromagnetic Spectrum

1. Radio waves: harm body cells, prevalence of migraine, headache disorders

5. Ultraviolet: damage to surface cells (including skin cancer) and blindness

2. Microwaves: internal heating of body tissue

6. X-rays: damage to cells

3. Infrared: skin burns

7. Gamma rays: cancer, mutation

4. Visible light: increased rates of premature skin aging and skin cancer

Mr Ng Han Guan Guru Cemerlang Physics MSAB

1.7.4

Form 5 Chapter 1: Wave Date:

Wave in Telecommunication

1. Sound waves cannot travel far. So, a very efficient way to send a voice signal is by using the carrier wave. 2. Modulation is the process where the sound signal is combined with the carrier wave. 3. The two most common types of modulation used in radio broadcasting are i.

Amplitude modulation (AM)

ii. Frequency modulation (FM)

1.7.5

FM and AM

1. FM waves have higher frequencies and more energy than AM waves. 2. FM waves penetrate the atmosphere instead of being reflected back to the Earth. 3. FM waves do not travel as far as AM waves. 4. FM waves are usually received clearly and produce a better sound quality than AM waves. 5. Wideband FM receivers are inherently less sensitive to noise.

16 3rd edition ÂŠ 2011 | chp 2 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan