Transcript Lesson notes (Powerpoint)

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Unit G9
Waves
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Lesson 1
What are waves?
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Aims
• Describe waves and their properties
• Understand the words crest, trough,
longitudinal, transverse, amplitude, and
wavelength
• Give some examples
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Mexican & Slinky Demos
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Copy notes
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• 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
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Drawing
• Draw two diagrams, one showing a
longitudinal wave the other showing a
transverse wave
• See Milner page 118 for some examples
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Wave Diagrams
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• Look on p114 of Milner
• Write a definition for amplitude and for
wavelength
• Include a diagram like this one …
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crest
wavelength
1.4
1.3
Microwaves
amplitude
1.2
1.1
1
0
0.5
1
1.5
2
0.9
0.8
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0.7
0.6
trough
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Worksheet
• Complete worksheet
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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?
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Aims
• Describe waves and their properties
• Understand the words crest, trough,
longitudinal, transverse, amplitude, and
wavelength
• Give some examples
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Lesson 2
The Wave Formula
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Aims
• Understand the word ‘frequency’
• Know and use the wave formula
• Know how amplitude and frequency affect
wave speed
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Demo
Frequency/speed using slinky/rope
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Copy notes
• Frequency is the number of vibrations that
the source makes every second
• It is measured in Hertz (Hz)
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• Speed tells us how quickly the energy goes
from one place to another
• It is measured as usual in m/s
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Formula
• If 5 waves are made every second and each wave
is 2m long, that makes ___ m of wave per second
• So if frequency=5Hz and wavelength=2m the
speed is 10m/s
• So the formula must be …
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Speed (m/s) = Frequency (Hz) x Wavelength (m)
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Wave Formula Practice
• Complete worksheet
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Practical
• Follow instructions on practical sheet
• You clear up any mess before leaving!
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Aims
• Understand the word ‘frequency’
• Know and use the wave formula
• Know how amplitude and frequency affect
wave speed
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Lesson 3
Water, sound and light
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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
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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
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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
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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
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Refraction
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• 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)
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Copy diagram
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Do light & sound work like
water waves or like particles?
• Complete the table together:
Light
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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
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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
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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
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Lesson 4
The Electromagnetic Spectrum
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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
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Demo
OHT spectrum
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Copy notes
• Light waves can have different wavelengths
– Short waves look blue to us
– Long waves look red to us
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R – longer waves
O
Y
G
B
I
V – shorter waves
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Copy notes
• Light waves can be made with even longer
or shorter wavelengths but we can’t 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
can’t)
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Draw
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• 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
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Practical
• Carry out the instructions on the sheet
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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
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Lesson 5
Uses of EM Waves #1
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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
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Copy notes
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• When waves hit an object they are:
– reflected,
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– absorbed or
– transmitted.
• Depending on the type of wave and
material this can be useful
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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 …
red
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When looking
in the body …
When scanning
bags …
X-rays
absorbed by …
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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)
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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
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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
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Lesson 6
Uses of EM Waves #2
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Aims
• Explain the uses of radio waves
• Explain the uses of different wavelengths of
microwaves
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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)
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Microwaves – copy
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• 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
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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
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Homework
• Next lesson you will need a pair of
headphones like the ones used for an iPod
or MP3
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Aims
• Explain the uses of radio waves
• Explain the uses of different wavelengths of
microwaves
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Lesson 7
Communications
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Starter – recap
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1.
2.
3.
4.
5.
Give three uses for microwaves
Which waves have the longest wavelength?
Which waves have the highest frequency?
Which waves can pass down optical fibres?
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?
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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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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
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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
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Animations
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• Draw the AM animation – this one will be
in the exam
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(P1b swf files)
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Building an AM receiver
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This part of the circuit tunes-in to the
radio station you want to receive
This part of the circuit filters
out the radio signal to leave
the original sound
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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
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Copy notes/diagrams
• Digital signals are signals that are either on
or off
Analogue
Digital
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Converting analogue to digital
• Step 1: Sampling the analogue signal
• Step 2: Convert samples to 0’s and 1’s
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• Step 3: Transmit a long string of 0’s and 1’s
(P1b pulse code mod)
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Digitising
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4
6
7
11
6
2
0100
0110
0111
1011
0110
0010
1
0.5
0
1
2
3
4
5
6
7
8
9
10
11
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14
15
16
17
18
19
20
21
22
23
24
0100 0110 0111 1011 0110 0010
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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)
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Copy
• When a digital signal is boosted it can be cleanedup at the same time
• All the 0.1’s are turned back into 0’s
• All the 1.1’s/0.9’s are turned back into 1’s
• The signal quality remains perfect
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• Draw noisy analogue and digital signals from
animation – explain why digital is better
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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
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Homework
• Transmitting signals sheet