© Boardworks Ltd 2003 KS4 Waves : Sound. © Boardworks Ltd 2003 A slide contains teacher’s notes wherever this icon is displayed - To access these notes

© Boardworks Ltd 2003

KS4 Waves : Sound


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What causes sound?

Take a tuning fork and strike it against a block of wood, what do you observe?

The tuning fork vibrates and you hear a sound.

All sounds are caused by vibrations.


Music

What vibrates when you sing?

Your voice-box.

What vibrates when you play a violin?

The strings


Sound waves are vibrations and so need a substance to travel through.

With air inside, the sound can be heard.

With nothing inside [a vacuum], the sound can’t be heard.

The Bell-jar experiment

What happens when the air is removed from the bell-jar?


Sound : How fast does it travel?

You need a quiet open space at least 100m long to perform this investigation.

> 100m

00:0000

START

00:0034

STOP

1) When you see the cymbals crash, press START.

2) When you hear the cymbals crash, press STOP.

Write your results in a table like this:


TryDistance

[m]Time

[s]Speed[m/s]

1. 100 0.34 294

2.

3.

4.

Calculate your average speed of sound :

Av. = [try 1 + try 2 + try 3 + try 4] 4.

What errors could have crept into your results?



Sound : What does it need to travel?

Sound waves need particles in order to travel.

The substance that the sound travels through affects the speed of sound greatly.

330 350

1450

5000

6000

0

1000

2000

3000

4000

5000

6000

7000

Air at 0 C Air at 30 C Water Concrete Steel

Material

Sp

eed

of s

ou

nd [m

/s]


Travelling sound

Sound travels by particles vibrating.

To understand this better you need to remember what the particles look like in a solid, liquid and a gas:

solid liquid gasIn which state are the particles closest together?

In which state are the particles furthest apart?solid

gas

Which state does sound travel fastest through?

Why?

Sound travels fastest through solids because the particles are closer together than in a liquid and a gas, so the vibrations are more easily passed from particle to particle.



Most of us have seen thunder storms - which comes first, the thunder or lightning?

The lightning gets to our eyes before the thunder reaches our ears.

1) Thunder & lightning are made at the same time so we deduce that light travels much faster than sound.

2) In fact light travels so fast that:

the time between seeing the flash and hearing the bang = time taken for sound to travel.


Reflection : Echoes

You should remember that sound is produced by a vibration and travels as a longitudinal wave

………..and that sound travels at different speeds through different substances [or media]

Sound waves reflect off hard, smooth surfaces to produce echoes.


Using echoes

What do we call reflected sound? An echo

Which surfaces are the best at reflecting sound:

HARD or SOFT ?

How are echoes reduced in cinemas and theatres?

By using soft materials on the walls such as curtains.

Name two animals that use echoes?

Bats and dolphins


Reflection : Echoes

Stand at least 100m from a large, straight wall.

Measure the distance from you to the wall.

Use a starting pistol [or clapper board] to make a sound.

Measure the time taken between firing the pistol and hearing the echo.

Remember, this is

‘two way travel time’ [twtt]

STARTSTOP

150m


The sound takes 0.92s to travel 300m.

Remember the formula for speed?

SPEED = DISTANCE TIME v = 300 0.92

v = 326 m/s

For the Higher Tier paper you will need to be able to change the subject of the formula.

Repeat this several times to obtain an average.

Reflection : Echoes


Reflection : Questions

Distance

[m] Time

[s] Speed [m/s]

Small aeroplane

600 5

Jet fighter 900 2

Meteorite 10,000 0.35

Cheetah 50 2.5

Which of these travel faster than the speed of sound in air?

120

450

28571

20


Studying sound

Signal generators can produce signals over a range of frequencies and of varying amplitudes.

Loudspeakers convert the signal from the signal generator into sound waves.

The oscilloscope allows us to study the frequency and loudness of a sound.


Pitch (or frequency)

A high pitch sound A low pitch sound.

The shorter/longer the wavelength of the wave on the trace; the lower/higher the frequency of the sound.

The more waves you can see, the higher the pitch/frequency.


Oscilloscope traces

Which trace represents the highest pitched sound?

A B

‘A’ is the highest pitched sound because it has the shortest wavelength/most number of waves visible.


Loudness

A quiet sound A loud sound

The larger/smaller the amplitude of the wave on the trace; the louder/quieter the sound.

The bigger the waves you can see, the louder the sound.


Oscilloscope traces

Which trace represents the loudest sound?

A. B.

‘B’ is the loudest sound because it has the largest amplitude, the larger the amplitude the more energy a wave has, the more

energy it has, the louder the sound.


Wave animation


Sound : What can I hear?

Increase the frequency of the signal provided by a signal generator whilst keeping the volume the same.

The lowest frequency I can hear is ________ Hz

The highest frequency I can hear is ________ Hz

20

20 000


Sound : Are we all the same?

You have just found your hearing range - could everyone hear exactly the same frequencies as you?

We all have slightly different hearing ranges but almost 1 in 5 people suffer some sort of hearing loss.

Temporary hearing loss may be caused by ear infections and colds and hearing recovers.

Permanent hearing loss and deafness can be present at birth or occur if the ear is damaged or diseased.


Sound : Are we all the same?

Hearing is tested using an audiometer and the results are shown on an audiogram.

0

10

20

30

40

50

60

70

80

0 2000 4000 6000 8000

Frequency of sound [Hz]

optimalhearing

impairedhearing

Heari

ng

Loss

[d

B]


Sound : Hearing Ranges

0 1 10

10

0

1,0

00

10

,00

0

10

0,0

00

1,0

00

,00

0

Frequency [Hz]

Hearing Ranges of Animals

Which animal can hear the lowest frequency?

Which animal can hear the highest frequency?

mothspigeons

moths

mice

pigeons

humans

elephants

bats


Sound : The ear

1. Sound waves are collected by the ear lobe or pinna.

2. The waves travel along the ear canal.

3. The waves make the ear drum vibrate.

4. The small bones [ossicles] amplify the vibrations.

5. The cochlea turns the vibrations into electrical signals.

6. The auditory nerve takes the signals to the brain.


Sound : How loud are sounds?

150

140

120

100

80

60

40

20

10

0

Permanent ear damage

Can just be heard

Aircraft overhead Personal stereo

A circular saw at 2m

Loud bell

Pin being dropped

Quiet countryside


What is noise?

A noise is any unwanted sound. What you might not consider noise, loud music for example, other people might!

What are the effects of noise?

1. _________

2. _________

3. _________

4. _________Nausea

Vomiting

Headaches

Deafness

How can you reduce the effects of loud noise?

1._________________

2._________________

3.____________________ _____________________

Ear protectors

Putting noisy machinery in insulated rooms

Double glazing


Using Sound Waves : Ultrasound

Our ears can’t detect frequencies above 20 kHz.

Sound above 20 kHz is called ULTRASOUND.


X rays are more energetic and penetrating and are a lot more dangerous, they could cause damage to the growing baby.Why do doctors use ultrasound to scan the foetus and not X rays which give a clearer picture?

Ultrasound has many uses, especially in medicine where it is used to scan the fetus.

10 weeks 20 weeks




Use the internet or research books to find out about other uses of ultrasound.

These search terms should help:

dolphin

ultrasonic toothbrush

jewellery cleaning

scans

SONAR

kidney stones

echo location

bats

ultrasonic cleaning


How ultrasound is used?

Ultrasound like all sound is reflected different amounts by different materials.

A receiver can be used to detect the amount of ultrasound reflected or lost from a signal.

A computer can then be used to build up an image of these ultrasound signals.

This is how ultrasound is used in prenatal scanning and industrial quality control.


What is the upper range of human hearing?

A. 20 Hz

B. 200 Hz

C. 2 000 Hz

D. 20 000 Hz


What causes all sounds?

A. Vibrations

B. Reflections

C. Refractions

D. Heat


Which of the following can sound not travel through?

A. Liquid

B. Vacuum

C. Solid

D. Gas


A ship releases an echo sounding and 4 seconds later receives a signal from the seabed, how deep is the sea? (speed of sound in water is 1500 m/s)

A. 6000m

B. 375m

C. 750m

D. 3000m


Which of the following is not a use of ultrasound?

A. Prenatal scanning

B. Quality control in industry

C. Cleaning delicate machinery

D. Cooking food

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© Boardworks Ltd 2003 KS4 Waves : Sound. © Boardworks Ltd 2003 A slide contains teacher’s notes wherever this icon is displayed - To access these notes