year 11 world communicates

8/20/2019 Year 11 World Communicates

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Physics: The World Communicates

Rebecca Duong

PHYSICS: THE WORLD COMMUNICATES 1

Task Outcome 1: The wave model can be used to explain how current technologies transfer information.

Describe the energy transformations required in one of the following:

- mobile telephone

- fax/modem

- radio and television

Mobile Telephone:

Sound energy: we speak into the microphone of a phone with our voices

Electrical energy: our voice is transformed into digitized electrical signals (binary)

Electromagnetic energy: signals are transmitted as radio waves to a base station where a system of antennae on

towers or tall building accepts them

Electrical energy: EM wave is transformed back and runs through the base station where the signal is amplified

again and the base station act as a transmitter

Electromagnetic energy: antenna transmits the wave through the air again

Electrical energy: the other phone’s antenna captures the wave and converts it

Mechanical energy: the energy is converted into sound by the speaker in the phone

Describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of

the wave and the medium

Waves are travelling vibrations or disturbances that transport energy without transporting matter

A pulse is a single disturbance travelling from one point to another

They are caused by a vibration or disturbance and transfer the disturbance and energy to other bodies but the

medium does not move forward

One dimension waves: wave along a line e.g. motion of a longitudinal wave in a slinky where the medium confines

the wave to the slinky so the energy of wave motion has only one dimension to travel

Two dimension waves: wave on a plane e.g. a pebble thrown into a still pond produces a transverse wave travelling

outward and away with a two dimension circular wavefront


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Rebecca Duong

2 PHYSICS: THE WORLD COMMUNICATES

Three dimension waves: waves through a 3D space e.g. the point source of sound (e.g. when we speak) and light

(e.g. light from a lamp) result in waves that immediately travel away from the source in 3 dimensions with spherical

wavefronts

Identify that mechanical waves require a medium for propagation while electromagnetic waves do not

Medium is the material through which mechanical waves are propagated

Mechanical waves require a medium or material for their propagation since the transfer of energy occurs through

the motion of the particles in the medium

Electromagnetic waves do not require a medium for propagation since they self propagate through perpendicular

electric and magnetic fields

Define and apply the following terms to the wave model: medium, displacement, amplitude, period, compression, rarefaction,

crest, trough, transverse waves, longitudinal waves, frequency, wavelength, velocity

Medium: the material through which mechanical waves are propagated

Displacement: distance of a particle from its rest or equilibrium position (y-axis)

Amplitude: maximum displacement of a particle from its rest position and corresponds to a crest

Period: time taken for one complete wave to pass any point or one complete oscillation of a point on the wave

Compression: zones of higher pressure where the particles of the medium are pushed closer together

Rarefaction: zones of lower pressure where the particles of the medium are spread further apart

Crest: highest points on the wave

Trough: lowest points on the wave

Transverse waves: particles in the medium vibrate perpendicular to direction of propagation or energy transfer

Longitudinal waves: particles in the medium vibrate back and forth parallel to the direction of propagation

Frequency: number of waves to pass a given point per second and is also the number of complete vibrations of a

point on a wave (Hertz)

Wavelength: distance between two adjacent corresponding points of a wave e.g. between two crests or troughs or

two compressions or rarefactions

Velocity: the product of frequency and wavelength


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Rebecca Duong


Describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal

waves

Transverse waves:

Particle motion: oscillates up and down

Direction of energy propagation: perpendicular to particle motion

Longitudinal waves:

Particle motion: vibrates back and forth

Direction of energy propagation: parallel to particle motion

Quantify the relationship between velocity, frequency and wavelength for a wave: v = f λ

Velocity of a wave is equal to frequency times wavelength

= where f is in Hz, is in metres and v is in ms-1

Perform a first-hand investigation to observe and gather information about the transmission of waves in:

- slinky springs

- water surfaces

- ropes

or using appropriate computer simulations

Present diagrammatic information about transverse and longitudinal waves, direction of particle movement and the direction

of propagation

Transverse waves:


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Longitudinal/Push waves:

Analyse information from displacement-time graphs for transverse wave motion

Perform a first-hand investigation to gather information to identify the relationship between the frequency and wavelength of

a sound wave travelling at constant velocity

A spring is used and the amount of time taken for a period to be completed is used to find frequency

A standing wave allows us to measure the wavelength

Frequency is inversely proportional to wavelength

As wavelength increases, the frequency decreases


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Rebecca Duong


Task Outcome 2: Features of a wave model can be used to account for the properties of sound.

Identify that sound waves are vibrations or oscillations of particles in a medium

Sound waves are longitudinal mechanical waves

Requires a medium for propagation hence their particles vibrate back and forth

Relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them

Compressions are high pressure, rarefactions are low pressure

If pressure was graphed, compressions will be equivalent to crests, rarefactions will be equivalent to troughs

Explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

The higher the pitch, the greater the frequency of the sound wave

The lower the pitch, the lower the frequency of the sound wave

As the volume of a sound increases, the amplitude of the sound wave that created it also increases

Amplitude is the maximum displacement of a given molecule from its mean position hence the larger the

displacement, the greater the amount of energy required to produce it

Low Pitch and High Pitch Loud/Soft

Explain an echo as a reflection of a sound wave

The lower the pitch, the lower the frequency of the sound wave

An echo occurs due to the reflection of a sound wave from the surface of an object or material

As the sound wave reaches the end of its medium, it reflects and travels back towards the source

Incident wave bounces off the surface and the observer hears the reflection of the original sound some time

afterwards

Most effectively reflected from hard, smooth surfaces while soft, irregular surfaces absorb the most sound

Describe the principle of superposition and compare the resulting waves to the original waves in sound

The Principle of Superposition states that if two or more waves pass through the same medium at the same time the

displacement of any point is the sum of the individual displacement of each wave at that point

Superposition of waves result in a new amplitude only, the frequency is not affected

Waves out of phase: amplitude of produced wave is less than either of the original waves

Waves in phase: amplitude of the produced wave is greater than either of the original waves

Perform a first-hand investigation and gather information to analyse sound waves from a variety of sources using the Cathode

Ray Oscilloscope (CRO) or an alternate computer technology


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Perform a first-hand investigation, gather, process and present information using a CRO or computer to demonstrate the

principle of superposition for two waves travelling in the same medium

Present graphical information, solve problems and analyse information involving superposition of sound waves


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Rebecca Duong


Task Outcome 3: Recent technological developments have allowed greater use of the electromagnetic spectrum.

Describe electromagnetic waves in terms of their speed in space and their lack of requirement of a medium for propagation

Electromagnetic waves are waves that do not require a medium to propagate

They propagate through changing and interacting electric and magnetic fields that are perpendicular to each other

They travel at the speed of light 3.00 x 108 ms-1

Identify the electromagnetic wavebands filtered out by the atmosphere, especially UV, X-Rays and gamma rays

Gamma rays: absorbed by the thermosphere

X-Rays: absorbed by the thermosphere

UV Rays: atomic oxygen and molecular nitrogen absorb high energy UV in the thermosphere while ozone absorbs

low energy UV in the stratosphere

Visible light: not filtered by the atmosphere

Infra-Red: mostly absorbed by the atmospheric gases

Microwaves: pass through the atmosphere

Radio waves: short wavelength radio waves pass through the atmosphere while long wavelength radio waves are

filtered out


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Identify methods for the detection of various wavebands in the electromagnetic spectrum

Gamma wave: Geiger counters, thermoluminescent detectors, X-ray film

X-Rays: X-ray film, electronic detectors and counters, Geiger counters

UV Rays: certain crystals that fluoresce under UV light, electronic photo-detectors, photomultipliers

Visible light: photoreceptors in eyes, electronic photo-detectors, light meters, photographic film, photomultipliers

Infra-Red: thermoreceptors in skin, thermocouples, electronic photo-detectors

Microwave: mobile phones, TV and satellite antennas, materials that fluoresce when exposed to microwaves

Radio wave: TV and radio aerials and antennas

Explain that the relationship between the intensity of electromagnetic radiation and distance from a source is an example of

the inverse square law: ∝1

2

Intensity is a measure of the amount of energy per unit of area

Intensity of a wave will decrease as you move away from the source

Light emanating from a point source spreads out in all d irections and travels at a constant speed, the energy of the

light will spread out in spheres

∝1

2 is the intensity of a uniformly transmitted wave with no mechanical energy loss decreases with the square

of the distance d from the source

Electromagnetic waves do not require a medium to propagate and in air there are practically no energy losses

Outline how the modulation of amplitude and frequency of visible light, microwaves and/or radio waves can be used to

transmit information

Modulation is the process of changing characteristics of a wave to add a signal to the carrier wave allowing useful

information to be transmitted

By altering either frequency, amplitude or phase of a carrier wave, the wave can act as a type of “code” to be

decoded and used

Information is added on a carrier wave by superimposing signals of varying frequency or signals of varying amplitude

but phase is rarely used

FM: frequency modulation, AM: amplitude modulation

Bandwidth: the range in which a modulating signal is limited to a narrow band of frequencies which is on either side

of the carrier frequency

Modulation of radio waves

Information broadcasted need to be limited to a band of frequencies ranging from 20Hz to 20000Hz

Each station is given a carrier wave of a particular broadcast frequency (tuning frequency)

A modulating signal is superimposed onto an unmodulated carrier of a certain frequency to produce a modulated

carrier

Modulating signal: the wave that contains the information to be sent


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Unmodulated carrier: wave that has the frequency it is transmitted at

Amplitude/frequency modulation: information required in the modulating signal is encoded in the

amplitude/frequency of the carrier wave

Demodulation: when the receiver receives the signal and subtracts the carrier wave from the modulated signal

Discuss problems produced by the limited range of the electromagnetic spectrum available for communication purposes

These restrictions are not placed on technologies which use optical fibres

Small bandwidth:

Small bandwidth in the EM range that can be used to effectively transmit signals

Causes congestion of frequencies leading to interference or no possible frequency which to transmit

As more and more people use these services, they will become more and more congested until the communication

network can no longer be supported by the narrow bandwidth

Health concerns:

Non-ionising EM poses significant health risks

Microwave radiation used in mobile phones is thought to create brain tumours and cause cancer

Perform a first-hand investigation and gather information to model the inverse square law for light intensity and distance from

the source

A light meter is used to record the intensity of light from various distances from a light source

A intensity vs. distance graph is constructed: very steep exponential relationship, possible intensity proportional to

some power of the distance

A intensity vs.1

2 graph is constructed: inverse exponential relationship, almost a positive linear function


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Rebecca Duong

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PHYSICS: THE WORLD COMMUNICATES

Identify the waves involved in the transfer of energy that occurs during the use of one of the following:

- mobile phone

- television

- radar

Mobile phone:

Sound wave (microphone) electrical energy (mobile phone) EM radiation (radio waves)(receiving cell tower)

electrical energy light (optical fibre)

Process continues in reverse to the receiver

Identify the electromagnetic spectrum range utilised in modern communication technologies

Communication: radio waves, microwaves, infra-red, visible light and UV

Radio waves: television, FM and AM radio, radar, some mobile telephone signals

Infra-red: telecommunications through optical fibres

Visible light: communication in fibre optic telecommunications and smoke signals


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Task Outcome 4: Many communication technologies use applications of reflection and refraction of electromagnetic waves.

Describe and apply the law of reflection and explain the effects of reflection from a plane surface on waves

Reflection is a wave property and can be described as waves bouncing off a surface, and thus is when a wave strikes

a boundary and is cast back into the medium in which it was originally travelling

Law of reflection: when waves reflect from a surface, the angle of incidence (i) is equal to the angle of reflection (r)

When waves are reflected, incident and reflected waves have the same frequency, wavelength and speed

Incident ray, reflected ray and normal all lie in the same plane

Angle of incident and angle of reflection are measured from the normal

Describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer

Reflection of light: fibre optics and CDs

Fibre optics allow massive amounts of information transfer over long distances

Reflection of radio waves: reflected off the ionosphere and used by television and radio

Describe one application of reflection for each of the following

- plane surfaces

- concave surfaces

- convex surfaces

- radio waves being reflected by the ionosphere

Plane surfaces:

Plane mirrors are a flat glass sheet over a silver backing and are highly reflective smooth surfaces

Forms images of objects that are in front of the mirror

e.g. CDs where laser beams are either reflected or not

Concave surfaces:

Concave mirrors magnify an image when the object is inside the focal point

Useful when trying to look at an object in greater detail e.g. dentists, make up mirrors

Reflects all focal rays parallel to the principal axes, allowing for a directed beam of light e.g. torches, car headlights

Convex surfaces:

Convex mirrors create virtual images diminished in size

Gives a wider field of vision e.g. driving mirrors, shopping centres, car rear-view mirror, carparks

Parallel rays incident on their surface reflect and diverge from a focus behind the mirror

Radio waves being reflected by the ionosphere:

Ionosphere: layer of ionised air approximately 50km to 640km above Earth’s surface and is ionised by UV radiation

Can absorb, reflect or allow some radio waves coming from earth to pass through

Low frequency or long wavelength waves reflect well Radio waves like light travel in straight lines and bounce off the small curvature of the atmosphere


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Higher frequency waves require a “line of sight” relationship between transmitter and receiver or they can be sent

to communication satellites and are relayed to another point such that multiple reflections between ground and

satellite stations allow the signal to travel around earth

Explain that refraction is related to the velocities of a wave in different media and outline how this may result in the bending of

a wavefront

Refraction is a wave property which describes the change in speed which occurs when light passes between any two

different materials of different densities

During refraction: frequency is constant, wavelength changes, velocity changes

Angle of incidence (i) is defined as the angle between the incident ray and the normal

Angle of refraction (r) is defined as the angle between the refracted ray and the normal

When waves travel into a relatively denser medium: ray bends towards the normal, i > r and wavelength and

velocity becomes smaller (slower)

When waves travel into a relatively less dense medium: ray bends away from the normal, i < r and wavelength and

velocity becomes greater (faster)

Medium 2 is denser than Medium 1 Medium 2 is less dense than Medium 1

Define refractive index in terms of changes in the velocity of a wave in passing from one medium to another

Relative refractive index of a medium: measure of how much velocity of light will change as it passes from one

medium to another

=

as the light ray goes from a to b ( ↑ = lower light speed, ↓ = higher light speed)


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Rebecca Duong


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Define Snell’s Law:v

v2=

sini

sinr

Snell’s Law states the ratio between the sine of the angle of incidence and the sine of the angle of refraction is a

constant, and is equal to the ratios of the velocity of light through the media

=

=

=

=

sin

sin where is the relative refractive index

Identify the conditions necessary for total internal reflection with reference to the critical angle

Critical angle () is the angle of incidence for which the angle of refraction is 90°

Critical angle only exists going from a more dense medium to a less dense medium

=

sin

sin=

sin

sin90° ∴ =

If the angle of incidence is greater than the critical angle (i > ic) then the wave will be “totally internally reflected”

Outline how total internal reflection is used in optical fibres

Total internal reflection describes the behaviour of light when it is reflected without refraction

Occurs when the angle of incidence of light as it is going from a denser medium into a less dense medium exceeds

the critical angle

Fibre optic cables are thin flexible rods that transfer information via light waves

Consist of two concentric layers of ultra pure, bubble free glass (fibre core and cladding)

Fibre core has the highest refractive index, cladding with a relatively lower reflective index, sheath protects the

inner layers to ensure no unwanted light enters the fibre and disrupts the signal

The refractive index of the fibre core must be greater than the cladding for total internal reflection to occur

Used for communication, doctor endoscopes and surgeons


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Perform first-hand investigations and gather information to observe the path of light rays and construct diagrams indicating

both the direction of travel of the light rays and a wave front

Use ray diagrams to show the path of waves reflected from:

- plane surfaces

-

concave surfaces

- convex surfaces

- the ionosphere


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Perform an investigation and gather information to graph the angle of incidence and refraction for light encountering a

medium change showing the relationship between these angles

Perform a first-hand investigation and gather information to calculate the refractive index of glass or Perspex

A light box is used to produce a narrow beam of light and directed into a Perspex block

Rays are traced and angles of incidence and refractions are measured

A sine of refraction vs. sine of incidence graph is constructed

A linear relationship is shown, with the gradient of the line of best fit showing1

Sin r is proportional to sin i

Refractive index of Perspex is 1.4


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Task 5: Electromagnetic waves have potential for future communication technologies and data storage technologies.

Identify types of communication data that are stored or transmitted in digital form

Digital form: data represented using binary code, a series of 1s and 0s

Uses: fax, internet, phone calls, text, picture, sound

Discuss some of the underlying physical properties used in one application of physics related to waves such as:

- Global Positioning System

- CD technology

- the internet (digital process)

- DVD technology

CD technology:

Compact discs are hard plastic disc which are metal coated then plastic coated

Data is stored in a continuous groove starting at the centre of the disc and spiraling outwards

An infrared recording laser of wavelength 780nm is focused onto the master disk and records digitized information

on the disk as a series of pits or small holes

“1” is represented by a deeper square pit while “0” is represented by lack of pits

Pits in the groove are about 0.5μm wide and up to 3μm long, separated by 1.6μm

When a CD is played, it rotates extremely quickly and a laser beam scans the surface of the disc so that the light is

either reflected from the metal surface or scattered by a pit

Optical sensors detect the light pattern produced and convert this to tiny digital pulses of electric current

Digital data is then converted to an analogue signal to produce pictures, videos and sound

year 11 world communicates

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