1. waves are carriers of energy
1. Current technologies associated with
information transfer may use waves of one form or another
waves are carriers of energy
images from SciArt
Describe the energy transformations required in one of the following: – fixed telephone – mobile telephone – fax/modem – radio and television – information storage systems
e.g. Transmitting a
voice message
on a mobile phone:
SOUND
ENERGY
ELECTRICAL
ENERGY
ELECTROMAGNETIC
RADIATION
(RADIO WAVES)
Soundtrack: “Bitter Sweet Symphony”

2. Waves are a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium

3. Features of a wave include frequency, wavelength and speed
‘medium’, ‘displacement’, ‘amplitude’, ‘period’, ‘compression’,
‘rarefaction’, ‘crest’, ‘trough’, ‘transverse waves’,
images from SciArt
for one source, f does not change when medium does
Given s vs t and s vs x can we work out v? l
v = f
what wavelength is 96.1 MHz???????

4. Electromagnetic waves are oscillating perpendicular
Mechanical waves require a medium for propagation while electromagnetic waves do not!
Electromagnetic waves are
oscillating perpendicular
electric and magnetic fields
All electromagnetic waves move at the speed of light
images from Microsoft Encarta

5. IN TRANSVERSE WAVES THE PARTICLES IN THE MEDIUM
Describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves
IN TRANSVERSE WAVES THE PARTICLES IN THE MEDIUM
MOVE PERPENDICULAR TO THE DIRECTION OF PROPOGATION
They move well through solids and on the surface of liquids but not through liquids or gases because of loose bonds between particles
IN LONGITUDINAL WAVES THE PARTICLES IN THE MEDIUM
OSCILLATE PARALLEL TO THE DIRECTION OF PROPOGATION
images from SciArt

6. sound waves are vibrations or oscillations of particles in a medium
2. Sound waves can be used to illustrate many of the properties of waves that are utilised in communication technologies
sound waves are vibrations or oscillations
of particles in a medium
discuss the effect of density of the medium on the transmission speed of sound waves
The velocity of sound in many other gases depends only on their density. If the molecules are heavy, they move less readily, and sound progresses through such a medium more slowly
images from SciArt
Sound generally moves much faster in liquids and solids than in gases. In both liquids and solids, density has the same effect as in gases; that is, velocity varies inversely as the square root of the density.

7. Relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves
AIR
PRESSURE
Explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

8. An echo is a reflection of a sound wave
Sonar, acronym for SOund Navigation And Ranging, a detection system based on the reflection of underwater sound waves— just as radar is based on the reflection of radio waves in the air. Distance is worked out from t assuming constant v in water

9. images from SciArt
describe the effect of different materials on the reflection and absorption of sound describe the transfer of energy involved in the absorption of sound

10. a trough, the waves cancel
Describe the principle of superposition and compare the resulting waves to the original waves in sound
When a crest meets
a crest, the waves add
When a crest meets
a trough, the waves cancel

11. All electromagnetic waves move at the speed of light
3. Recent technological developments have allowed greater use of waves in the electromagnetic spectrum that do not require a medium for propagation
All electromagnetic waves move at the speed of light
Electromagnetic
radiation exists at a
range of different
frequencies and
wavelengths - -
a whole SPECTRUM!
Electromagnetic radiation has some everyday uses and effects, including applications in communication technology
images from SciArt

12. e.g. eye or
photographic film
for light,
thermometer for
infra-red,
Geiger counter
for Gamma rays
Identify some methods of detection for a number of wave bands from the electromagnetic spectrum Explain that the penetrating power of electromagnetic waves is related to differences in frequency or wavelength
Low frequency electromagnetic radiation
penetrates the atmosphere better than high
frequency. e.g. sunsets look red because you
are looking at the light through more atmosphere
Explain that the relationship between the intensity of electromagnetic radiation and distance from a source (for a large distance) is an example of the inverse square law I prop. to 1/d 2.
Discuss limitations of the use of electromagnetic waves for communication purposes
Outline how the modulation of amplitude or frequency of visible light, microwaves and/or radio waves can be used to transmit information
AMPLITUDE
MODULATION
FREQUENCY
MODULATION

13. Caroline Chisholm College Physics
Electromagnetic radiation of different wavelengths is absorbed by different amounts in the atmosphere. Wavebands which are absorbed are therefore not easily detected from ground-based systems, so space telescopes (such as the Hubble Space Telescope) are preferable.
Very short wavelength radiation such as X-rays and Gamma rays
interact with and are absorbed by oxygen and nitrogen in the atmosphere
Most Ultraviolet (UV) radiation interacts with ozone and so cannot reach the ground.
Infrared radiation interacts with water vapour and carbon dioxide
and so is (incompletely) absorbed by the atmosphere
Long waves interact with electrons in the ionosphere
So only near-UV, visible light, near-Infrared, radio and microwaves
make it to the ground with out much absorption by the atmosphere.
All others are more easily detectable from space

14. 4. Many communication technologies use applications of reflection and refraction of electromagnetic waves
REFLECTION
ANGLE OF INCIDENCE=ANGLE OF REFLECTION
describe ways in which applications of reflection of light, radio waves and microwaves have assisted in information transfer
e.g. fibre optics, satellite dishes, radio telescopes, orbitting satellites etc.

15. Describe one application of reflection for each of the following:
plane surfaces
Bathroom mirror
SHOP MIRRORS
concave surfaces convex surfaces
images from SciArt
Radio waves can diffract around objects and are reflected by the ionosphere and the ground, so
they could be sent around the world even before there were satellites. However, reliability depends
on the time of the day, the position of the sun, solar winds and losses of intensity over distance.

16. Describe refraction in terms of the bending of the wavefront passing from one medium to another Explain that refraction is related to the different velocities exhibited by a wave in two media
images from SciArt

17. (angles always measured from normal) refractive index is the ratio of
v1 to v2
so if we know the refractive index when moving from medium 1 to medium 2,
we can compare the velocities of light in the two mediums
Define refractive index in terms of changes in the velocity of a wave in passing from one medium to another Define and discuss the application of Snell’s Law: v1/v2 = (sin i)/(sin r) = refractive index
(angles always
measured from normal)
Identify the conditions necessary for total internal reflection and determine critical angle Outline how refraction and/or total internal reflection are used in technologies such as lenses or optical fibres

18. e.g. CD DVD Computer disks
5. Other properties of 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
e.g. CD
DVD
Computer disks

19. Discuss the developments in technology that allowed the production of communication technologies, such as CD technology and Global Positioning Systems
e.g. CDs use electromagnetic radiation (laser light) to reflect off pits
in the CD surface. The intensity of the reflected light provides a
varying signal which is changed to a binary code of numbers which
can be used to create the signal amplitude of the music or video.