Unit G9

1
Unit G9

• Waves

2
Lesson 1

• What are waves?

3
Aims

• Describe waves and their properties
• Understand the words crest, trough, longitudinal,
  transverse, amplitude, and wavelength
• Give some examples

4
Mexican Slinky Demos
5
Copy notes

• Waves are vibrations that travel from one place
  to another
• The material that vibrates stays in its place,
  only the vibration energy moves
• There are two kinds of vibration
• in out called longitudinal
• up down called transverse
• Longitudinal waves travel parallel to the
  vibrations
• Transverse waves travel perpendicular to the
  vibrations

HT
6
Drawing

• Draw two diagrams, one showing a longitudinal
  wave the other showing a transverse wave
• See Milner page 118 for some examples

7
Wave Diagrams

• Look on p114 of Milner
• Write a definition for amplitude and for
  wavelength
• Include a diagram like this one

crest
wavelength
amplitude
trough
8
Worksheet

• Complete worksheet

9
Plenary qwik qwiz

1. Sound is made by a speaker. The cone moves in
   out. What kind of waves are sound waves?
2. The sound is made louder. The cone moves in
   out further. What would be different about a
   drawing of the waves?
3. John can see ripples on a pond. There are 5
   ripples in 1m. What is the wavelength?

10
Aims

• Describe waves and their properties
• Understand the words crest, trough, longitudinal,
  transverse, amplitude, and wavelength
• Give some examples

11
Lesson 2

• The Wave Formula

12
Aims

• Understand the word frequency
• Know and use the wave formula
• Know how amplitude and frequency affect wave speed

13
Demo

• Frequency/speed using slinky/rope

14
Copy notes

• Frequency is the number of vibrations that the
  source makes every second
• It is measured in Hertz (Hz)
• Speed tells us how quickly the energy goes from
  one place to another
• It is measured as usual in m/s

15
Formula

• If 5 waves are made every second and each wave is
  2m long, that makes ___ m of wave per second
• So if frequency5Hz and wavelength2m the speed
  is 10m/s
• So the formula must be
• Speed (m/s) Frequency (Hz) x Wavelength (m)

16
Wave Formula Practice

• Complete worksheet

17
Practical

• Follow instructions on practical sheet
• You clear up any mess before leaving!

18
Aims

• Understand the word frequency
• Know and use the wave formula
• Know how amplitude and frequency affect wave speed

19
Lesson 3

• Water, sound and light

20
Aims

• Describe in detail how refraction happens
• Draw and interpret ray and wavefront diagrams of
  reflection and refraction
• Describe situations where water waves, light and
  sound can all be reflected and refracted

21
Revision Reflection

• Light travels in straight lines
• It bounces off objects this is called
  reflection
• If the object is flat and smooth the incoming and
  outgoing angles are the same
• Draw red book p36 bottom

22
Revision Refraction

• Light changes direction if it goes into another
  material such as glass or water
• It changes direction because it changes speed

normal line
23
Year 8 Revision

• Set 3 and Set 2 (F) only
• Work through Milner p110-111
• Do all questions

24
Wavefront diagrams - copy notes

• A wavefront diagram is a birds-eye view, showing
  the crests of the waves

• The spacing is the wavelength
• The waves are moving at right angles to the
  wavefronts

Draw the wavefront diagram showing water waves
reflecting off a wall mark the wavelength in a
different colour
25
Refraction

• Refraction happens because the waves change speed
  in the new material
• This makes the waves bunch up as well as change
  direction
• The wavelength gets shorter because the waves
  slow down
• (beach.mov)
• (refr_anim.dir)

26
Copy diagram
27
Do light sound work likewater waves or like
particles?

• Complete the table together

Light Sound Snooker balls Water waves
Bounces off things (reflects)
Changes direction if it slows down (refracts)

• So refraction suggests light and sound are like
  waves, not balls

28
Aims

• Describe in detail how refraction happens
• Draw and interpret ray and wavefront diagrams of
  reflection and refraction
• Describe situations where water waves, light and
  sound can all be reflected and refracted

29
Homework

• Do the questions from the sheet
• Full answers in your book
• All drawings pencil and ruler or you will have to
  do them again

30
Lesson 4

• The Electromagnetic Spectrum

31
Aims

• List the regions of the electromagnetic spectrum
  in order
• Know how these waves are different from sound and
  water waves
• Know how their speed, wavelength and frequency
  change

32
Demo

• OHT spectrum

33
Copy notes

• Light waves can have different wavelengths
• Short waves look blue to us
• Long waves look red to us

R longer waves O Y G B I V shorter waves
34
Copy notes

• Light waves can be made with even longer or
  shorter wavelengths but we cant see them
• Light is one part of a family of electromagnetic
  waves
• They all travel at the speed of light
• They can pass through empty space (sound cant)

35
Draw

• Draw out the electromagnetic spectrum
• Put these words at the right ends
• long wavelength
• short wavelength
• high frequency
• low frequency
• Make up a mnemonic to remember
• RMIVUXG

36
Practical

• Carry out the instructions on the sheet

37
Practical

• Do these invisible waves really exist?
• Take out your phone yes, really!
• Go to camera and select night mode
• Your camera can now see infra-red waves as well
  as light waves
• To prove this, fire a remote control at your
  camera you cant see it flashing, but the
  camera can
• Now draw and describe what you did

38
Aims

• List the regions of the electromagnetic spectrum
  in order
• Know how these waves are different from sound and
  water waves
• Know how their speed, wavelength and frequency
  change

39
Lesson 5

• Uses of EM Waves 1

40
Aims

• Know what can happen when waves hit an object
• Explain the uses of X-rays
• Explain the uses of infra-red radiation
• Know the advantage of optical fibres

41
Copy notes

• When waves hit an object they are
• reflected,
• absorbed or
• transmitted.
• Depending on the type of wave and material this
  can be useful

42
X-rays copy and complete

• X-rays are transmitted by soft materials but
  partly absorbed by denser materials
• This makes them useful for looking inside the
  body, and for security scans at airports

X-rays pass through X-rays absorbed by
When looking in the body
When scanning bags
43
Infra-red copy and complete

• Infra-red (IR) rays come from all warm objects
• They are absorbed by the surface of most objects
  making them heat up
• Low power IR can be used to send signals
• Uses
• grills, house security sensors, remote controls,
  cable TV/telephone
• For each use, write one sentence about how it
  works (see Milner p137)

44
Practical SAFETY GOGGLES

• Copy notes
• Light and infra-red waves can be used for sending
  messages down optical fibres (e.g. phone calls,
  cable TV)
• This is better than using electric cables because
  there is very little loss of signal in the fibre
• Now follow the practical sheet
• VERY HOT OBJECTS
• BROKEN GLASS!
• WORK SAFELY AT ALL TIMES

45
Aims

• Know what can happen when waves hit an object
• Explain the uses of X-rays
• Explain the uses of infra-red radiation
• Know the advantage of optical fibres

46
Lesson 6

• Uses of EM Waves 2

47
Aims

• Explain the uses of radio waves
• Explain the uses of different wavelengths of
  microwaves

48
Radio copy

• Radio waves are very long (over 1m) and pass
  through most objects
• They are used to send the information for TV and
  radio programmes
• They are absorbed by metal aerials they make
  the electrons in the metal vibrate (making an
  alternating current)

49
Microwaves copy

• Microwaves are shorter than radio waves from a
  few mm up to 1m
• Some wavelengths are absorbed by water and are
  used to heat food
• Other wavelengths are used for signals e.g.
  satellite TV, mobile phones, Bluetooth, and
  wireless internet
• Metals reflect microwaves e.g. satellite dish,
  grille inside microwave door

50
Questions

• Complete the question sheet
• Use notes and Milner book to help you
• Answer all basic questions
• Questions marked need some lateral thinking
  (s are very awkward!)
• Go on to the (easier) summary sheet for uses of
  EM waves instead if you prefer

51
Homework

• Next lesson you will need a pair of headphones
  like the ones used for an iPod or MP3

52
Aims

• Explain the uses of radio waves
• Explain the uses of different wavelengths of
  microwaves

53
Lesson 7

• Communications

54
Starter recap

1. Give three uses for microwaves
2. Which waves have the longest wavelength?
3. Which waves have the highest frequency?
4. Which waves can pass down optical fibres?
5. Which waves heat up materials that absorb them?
6. What happens when microwaves hit a metal object?
7. What happens when radio waves hit a metal object?

55
Aims

• Know what an analogue signal is
• Explain how to make a wave carry information
• Know the job of a receiver

56
Copy notes

• Sound waves cannot travel very far before they
  lose strength (amplitude)
• To broadcast sounds we make a radio wave that is
  like the original sound and transmit the radio
  wave
• The radio signal is called analogue

57
Copy notes

• Analogue radio signals can be like the original
  sound in two ways
• An AM signal has an amplitude that is changed to
  be like the original sound
• An FM signal has a frequency that is changed to
  be like the original sound
• The receiver decodes the radio signal to get the
  original sound back

58
Animations

• Draw the AM animation this one will be in the
  exam
• (P1b swf files)

59
Building an AM receiver
60
Aims

• Know what an analogue signal is
• Explain how to make a wave carry information
• Know the job of a receiver

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Lesson 8

• Digital Signals

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Aims

• Know what a digital signal is
• Explain how to convert analogue signals to
  digital codes and vice versa
• Explain the advantages of digital signals

63
Copy notes/diagrams

• Digital signals are signals that are either on or
  off
• Analogue Digital

64
Converting analogue to digital

• Step 1 Sampling the analogue signal
• Step 2 Convert samples to 0s and 1s
• Step 3 Transmit a long string of 0s and 1s
• (P1b pulse code mod)

65
Digitising

• 4 0100
• 6 0110
• 7 0111
• 11 1011
• 6 0110
• 2 0010
• 0100 0110 0111 1011 0110 0010

66
Why bother? copy notes

• As waves travel
• they get weaker (lose amplitude)
• interference (noise) gets added
• When signals are boosted the noise gets worse as
  well
• The signal quality gets worse and worse
• (P1b a-to-d)

67
Copy

• When a digital signal is boosted it can be
  cleaned-up at the same time
• All the 0.1s are turned back into 0s
• All the 1.1s/0.9s are turned back into 1s
• The signal quality remains perfect
• Draw noisy analogue and digital signals from
  animation explain why digital is better

68
Aims

• Know what a digital signal is
• Explain how to convert analogue signals to
  digital codes and vice versa
• Explain the advantages of digital signals

69
Homework

• Transmitting signals sheet