physics from 5 chapter 1 wave

8/3/2019 Physics From 5 Chapter 1 Wave

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Equilibrium Position

An equilibrium position is a point where an oscillating object

experiences 0 resultant forces.

Complete Oscillation

A complete oscillation occurs when the vibrating object moves to

and fro from its original position and moves in the same direction as itsoriginal motion.


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Amplitude

Amplitude is the maximum displacement of an object from itsequilibrium position. The SI unit for amplitude is meter, m.

Period

Period is defined as the time required forone complete oscillation

or vibration.

Frequency

Frequency, f is the number of complete oscillations that take place

in one second.

The SI unit for frequency is hertz, Hz.

Important Formula:


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Displacement - Time Graph

From a Displacement - Time graph, we can find:

1. the amplitude

2. the period

3. the frequency

of an oscillation


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Natural Frequency

The Natural frequency of an oscillating system is the frequency of

the system when there is no external force acting on it.

Damping

Damping is the decrease in the amplitude of an

oscillating system.

An oscillating system experiences damping when its

energy is losing to the surrounding as heat energy.

The frequency of the system remains unchanged.

Graph of Damping

The Displacement - Time Graph

The Amplitude - Time Graph


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Internal and External Damping

Damping can be divided into:

external damping, where an oscillating system loses

energy to overcome frictional force or air resistance that act

on it.

internal damping, where an oscillating system losesenergy due to the extension and compression of the

molecules in the system.

Force Oscillation

In a damped oscillation, external force must be applied to the system

to enable the oscillation to go on continuously.

Oscillation with the help ofexternal force or forces is called a force

oscillation.


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Resonance

In a force oscillation, if the frequency of the external force is equal

to the natural frequency of the system, the system will oscillateswith maximum amplitude, and this is named as resonance.

Barton's Pendulum

When pendulum X oscillates, the other pendulums are forced to

oscillate. Pendulum D will oscillates with the largest amplitude.

Pendulum X and D have equal length and consequently equal natural

frequency. Therefore resonance happens to pendulum D, and itoscillates with maximum amplitude.


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Wave

A wave is a disturbance or variation that propagates

through a medium, often transferring energy. Waves travel and transfer energy (its amplitude) and

information (its frequency) from one point to another, with

no permanent displacement of the particles of the medium.

The particles of the medium are oscillate around an

almost fixed positions.

What is phase?

A phase is the current positionin the cycle of

something that changes cyclically.

Two vibrating particles are in the same phase if their

displacement and direction of motion are the same.

Wavefront


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A wavefront is a line or a surface that connects points that are moving

at the same phase and has the same distance from the source of the

waves.

Wavefront is always perpendicularto the direction of wave

propagation.

Wavelength

The wavelength (l) is defined as the distance between two successive

particles which are at the same phase (exactly the same point in their

paths and are moving in the same direction.).


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As shown in the diagram, A and B are in the same phase, therefore

the distance between A and B is the wave length of the wave.

Types of wave - Transverse Wave

A transverse wave is a wave where the particles of the mediumvibrate in a direction that is perpendicular to the direction of the wave

motion.

Example: Light wave, ripple, radio wave

Types of Wave - Longitudinal Wave

A longitudinal wave is a wave where the particles of the medium

vibrate in a direction that is parallel to the direction of the wave motion.

Example: Sound Wave


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Formula for velocity of wave

Reflection of Straight And Circular Wave

From Deep to Shallower Region

When plane waves move from deep to shallow water, their

wavelength become shorterand the velocity decreases.

The frequency of the wave remain unchanged.

This can be illustrated by placing a piece of rectangular Perspex of

suitable thickness in the tank to reduce the local water depth.


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Refraction of Water Wave

The change in wavelength and speed causes a change the waves

direction when they cross the boundary. In other words, refraction

occurs.

Refraction - Deeper to Shallower Region

When water waves are propagating from deeper region to a shallower

region, the wave will be refracted approaching the normal.


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Refraction - Shallower to Deeper Region

When water waves are propagating from shallower region to a deeper

region, the wave will be refracted away from the normal.

Some Other Pattern of Refraction


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Natural Phenomenon Involves Refraction

The effect of refraction causes seaside near to a cape is stony while

sea near to a bay is sandy.

At the middle of the sea, the wavefront is a linear line.

When waves move close to the coast line, the

wavefronts start to curve and follow the topography of the

coast line.

At the bay, the energy of the wave spread to a wider

area, and cause the amplitude to reduce. At the cape, the energy of the wave is converged to

a smaller area, therefore the amplitude of the wave

increases.

Diffraction

Diffraction is the spreading of a wave when it travels through an

opening or a small obstacle.


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Charecteristic of Diffraction

1. Wavelength does not change.2. Frequency does not change.

3. Speed of diffracted does not change.

4. The amplitude of the wave decreases after diffraction.

Diffraction happen when waves encounter an obstacle

Waves spread to a wider area after passing the

obstacle.

The wavelength and the frequency remain unchanged

after diffraction.

Diffraction happen when waves pass through anopening


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Waves spread to a wider area after passing through

the opening.

The wavelength and the frequency remain unchanged

after diffraction.

Factors Affecting the Magnitude of Diffraction -Wavelength

Shorter wavelength - Diffracted

less

Longer wavelength - Diffracted

more

In the diagram above, we can see that as the wavelength of a wave is

longer, it will be diffracted more compare with a wave with shorterwavelegth.


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Factors Affecting the Magnitude of Diffraction - Size ofOpening

Small opening - Diffracted more Bigger opening - Diffracted less

Diagram above shows that the magnitude of diffration will reduce

when the size of opening increases.

Principle of Superposition

The principle of superposition states that where two or more waves

meet, the total displacement at any point is the vector sum of the

displacements that each individual wave would cause at that point.


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Coherent Wave

Two wave sources which are coherent have the same frequency(therefore same wavelength) and in phase orconstant phase

difference.


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Interference

The effect of superposition of two coherent waves is interference.

Interference is the phenomenon when two or more waves overlap in

the same region of space at the same time.

Constructive interference


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Superposition of waves which have same phase (2 crest or 2 trough)

to produce a resultant wave which vibrates with maximum amplitude.

Destructive Interference

Superposition of waves which are anti-phase (crest and trough) to

produce a resultant wave which vibrates with minimum amplitude.

Node and Antinode


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An anti-node is a point ofmaximum amplitude where constructive

interference occurs. Whereas a node is point ofzero amplitude

where destructive interference occurs.

The anti-node line joins all anti-node points. The node linejoins all

node points.

Interference's Formula


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Sound Wave

Sound wave is a mechanical wave that requires a

medium for its propagation. Therefore sound wave cannotpropagate in vacuum.

The medium for propagation can be solid, liquid or

gas.

Sound waves propagate fastest in solid and slowest

in gas.

Sound Wave as a Longitudinal Wave

Sound wave is a series of compression and rarefaction of layers of

air molecules repeatedly through space.

The forward and backward vibration of the air molecules in the

direction of motion of a sound wave shows that sound is a

longitudinal wave.

Types of Sound Wave


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Human ear is capable of hearing sound with

frequency in the range of 20Hz 20,000Hz, and the sound

wave with frequency in this range is called an audio/Sonic

wave.

Sound wave with frequency lower than 20Hz is called

an Infrasonic Wave.

Sound wave with frequency higher than 20,000Hz is

called an Ultrasonic wave.

Infrasonic Audio/Sonic Ultrasonic

20 kHz

Speed of Sound Wave

Speed of sound wave in solids is greater than in

liquids, which is greater than in gases.

Speed of sound in air is not affected by pressure,

but is affected by the temperature.

As temperature increases, speed of sound in air

(and other gases) is also increases.

Sound usually travels more slowly with greater

altitude, due to reduced temperature.Speed of sound can

be calculated by the equation


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Pitch and Loudness

Loudness is influenced by the amplitude of the sound wave.The

greater the amplitude of sound wave, the higher the loudness of the

wave.

The pitch of a sound is high or low of the sound. The pitch of sound

is determined by its frequency. The higher the frequency, the higher

the pitch.


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Reflection of Sound Wave

The clicking sound of the stop watch can be heared clearly when the

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

Sound waves obey the law of reflection. That is, the angle of

incidence is equal to the angle of reflection.

Refraction of Sound Wave 1


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The amplitude of the sound wave increases when a balloon filled

with carbon dioxide is placed between the speaker and the

microphone.

Explanation:

Carbon dioxide is denserthan air.

The sound wave is refracted approaching the

normal when the wave propagates from the air into the

balloon, and away from normal when moving out from the

balloon.

As a result, the balloon acts as a biconvex lens and

converge the sound wave at a point.

Refraction of Sound Wave 2


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The amplitude of the sound wave decreases when a balloon filled

with helium gas is placed between the speaker and the microphone.

Helium gas is less dense than air. The sound wave is refracted away from the normal

when the wave propagates from the air into the balloon,

and closer to the normal when moving out from the

balloon.

As a result, the wave is diverged to a wider area and

causes the amplitude of the sound wave decreases.

Refraction - Natural Phenomenon


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The sound of a distance train is clearer at night.

Explanation:

At night, the air closer to the ground is coolerthan the air further

from the ground.

Sound wave travel slower in cool air. As a result, the sound wave is

refracted in the path of curve towards the ground instead of spreading

to a wider area (as at daytime).

Diffraction of Sound Wave

The street cleaner can hear the sound of the radio even though it is

behind an obstacle.


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Explanation:

The sound of the radio spreads around the corner of the wall due to

diffraction of sound wave.

Interference of Sound Wave

Alternating loud and soft sounds are detected as the microphone is

moved from left to right.

Explanation:

The two loud speakers are sources of two coherent sound waves as

they are connected to the same audio signal generator.


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The alternating loud and soft sounds are caused by interference of

the sound wave.

Formula of Interference

Wavelength of the sound wave is given by the equation

Properties of Electromagnetic Waves

Electromagnetic wave can travel in free space.

They travel in straight lines at a speed of

approximately 300000 km/s.

They are electric, magnetic and transverse in nature.


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Electromagnetic waves are electrically neutral.

Electromagnetic wave show characteristic of

polarization.

Polarisation of Transverse Wave

A transverse wave can be polarized. Plane polarized light will be produced when light

travels through a polarizing material like polaroid.


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Polaroid is a type of material that only allows light

waves of one plane to pass through. This means that only a

portion of the source light gets to pass through the polaroid.

Radio Wave

Source

Electrical oscillating circuit (consists of a capacitor and an conductor

connected in series)

Application

Telecommunications

Broadcasting: Radio and

television transmission

Astronomy study

Microwave

Source

Oscillating electrical charge in a microwave transmitter

Application

Satellite transmissions

Radar systems to detect objects (size, form and

position)

Cooking


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Infrared Radiation

SourceHot bodies, the sun and fires

Application

Night vision

Thermal imaging and physiotherapy

Remote controls for TV/VCR

Heating in physiotherapy

Thermometer

Cooking

Visible Light

Source

The sun, hot objects, fires, light bulbs, fluorescent tubes

Application

Sight

Photosynthesis in plants

Photography

Ultraviolet Light


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Source

Very hot objects, the sun, mercury vapour lamps

Application

Identification of counterfeit notes

Production of fluorescent effects

Production of vitamin D in the skin

Sterilisation to destroy germs

Pest control

Disinfecting drinking water

X-Ray

Source

X-ray tubes where high energy electrons bombarding a metal plate.

Application

Radiotherapy

Radiography (X-ray photograph)

Detection of cracks in building structures

Crystallography

Gamma Ray


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Source

Radioactive substances

Application

Cancer treatment

Sterilisation of equipment

Pest control in agriculture

Reflection of Light Wave

The characteristic of reflection of light enables us to see objects.

Objects that do not emit light are not seen in the dark.

An object only is seen if light is incident on it a reflected back to our

eyes.

Refraction of Light Wave

When light travels one medium to another of differing density, its

speed changes.


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Speed of light is higher in a medium of less density as compare with

one higher density.

The change in velocity of light when it travels from one media toanother of different density results in the refraction phenomenon.

Diffraction of Light Wave -Single slit experiment

Light is diffracted if it passes through a narrow slit.

Diffraction pattern is made up of the bright bands and

dark bands of different width.

The central band is wider and brighter. The dark and

bright bands of narrower width are alternatively observed

on the left and right side of the central bight band.

Conditions for diffraction to take place are:


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Light source must be monochromatic. That is, the light must possess

only one wavelength.

Slit size must be small enough as compare with the wavelength oflight.

Factors affecting the pattern of diffraction

Size of the slit - Smaller size, diffracted more

Colour of the light - Longer wavelength, diffracted more


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Distance of the screen from the slit

Young's Double Slit Experiment


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Young's double-slit is made up of two slits ruled on a piece of slide

and painted with 'aquadak'.

When monochromatic light passes through the

Young's double-slit, diffraction of light occurs and two

coherent sources (same amplitude, frequency and phase)

are produced as shown in the diagram above

The two coherent sources will overlap and superpose

to produce the effects of constructive and destructive

interference.

Constructive interference generates bright fringes

while destructive interference produces dark fringes.

Fringe size of bright fringes and dark fringes are

about similar in size. Fringe separation between any dark

fringe and a neighboring bright fringe which alternates in

position with the former is the same.

physics from 5 chapter 1 wave

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