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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• 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

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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

• Look on p114 of Milner

• Write a definition for amplitude and for wavelength

• Include a diagram like this one …

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

0 0.5 1 1.5 2

amplitude

wavelength crest

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)

• 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 …

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

• 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 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

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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

R – longer wavesOYGBIV – 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

• 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

• When waves hit an object they are:

– reflected,

– 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 …

X-rays absorbed by …

When looking in the body …

When scanning bags …

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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

• 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

1. Give three uses for microwaves2. 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?

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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

• Draw the AM animation – this one will be in the exam

(P1b swf files)

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Building an AM receiver

This part of the circuit tunes-in to theradio station you want to receive

This part of the circuit filtersout the radio signal to leavethe 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

• Step 3: Transmit a long string of 0’s and 1’s

(P1b pulse code mod)

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Digitising

4 01006 01107 011111 10116 01102 0010

0100 0110 0111 1011 0110 0010

0

0.5

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

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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 cleaned-up 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

• 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