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Waves: Sound

KS4 Physics


Waves: Sound

Contents

What is sound?

Sound and reflection

Hearing sound

Ultrasound

Structure of sound waves


What causes sound?

The tuning fork vibrates and you hear a sound.

Sounds are made when an object vibrates.

Take a tuning fork and strike it against a block of wood. What do you observe?


Good vibrations!

What vibrates so that the following make sounds?

violin strings drum

skin

voice box

loudspeaker cone


How does sound travel?

How does sound reach your ear?

When the drum skin is struck, it vibrates which causes the air beside the drum to vibrate.

The compression and stretching of air particles creates a sound wave which is carried through the air to your ear.

What type of wave is a sound wave?

longitudinal wave


Remove the air from the bell jar and what happens to the sound?

The bell-jar experiment

Place a ringing clock inside the bell jar and what happens?

There is air inside the bell jar so the sound can travel and be heard.

With a vacuum inside the bell jar, the sound cannot be heard. Why?

vacuum pump on


100 m

00:0000

START

00:0034

STOP

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

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

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

How fast does sound travel?


sound distance (m)

time(s)

speed(m/s)

1234

How are these values used to estimate the speed of sound?

Record the results of your sound experiments in a table.

=294 m/s distance

timespeed = = 100

0.34

100 0.34 294



Use the results of the cymbals experiment to calculate your average speed of sound.

How does your calculation for the average speed of sound compare with the real speed?

The speed of sound in air is about…

What errors could have affected the results of your cymbals experiment?

340 m/s

Do you think the speed of sound in water is the same as it is in air?



Different speeds of sound


Sound and states of matter

Sound waves need a substance to travel through.

What are all substances made of?

What is the particle model of a solid, a liquid and a gas?

In which state are the particles closest together?

In which state are the particles furthest apart?

solid

gas

particles

solid gasliquid


Sound and states of matter

Sound waves travel by particles vibrating.

What state does sound travel fastest through and why?

The particles in a solid are closer together than in a gas or a liquid. This means vibrations are more easily passed from particle to particle and so sound waves travels faster.

solid gasliquid

Sound waves travel fastest through solids.


Usually, you see lightning before you hear thunder . Light travels much faster than sound.

The speed of light is…

During a thunderstorm, thunder and lightning are created at the same time.

Which do you notice first?

How could you use thunder and the speed of sound to estimate how far away a thunderstorm is?

300 000 000 m/sHow much faster is light than sound?

Sound or light – which is faster?


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

distance (m)

time (s)

speed(m/s)

small aeroplane 600 5

jet fighter 900 2

cheetah 50 2.5

meteorite 10 000 0.35

120

450

28 571

20

The jet fighter and the meteorite break the sound barrier. What does this mean?

Breaking the sound barrier!


Waves: Sound

Contents

What is sound?

Hearing sound

Ultrasound




The sound wave is reflected back from the surface.

What type of sound does this produce?

What happens when a sound wave meets a hard flat surface?

echo

Reflected sound waves


1. Use a starting pistol (or clapper board) to make a sound.

2. Measure the time taken between firing the pistol and hearing the echo. How far does the sound travel?

START

150 m

Stand at least 100 m from a large, flat wall with a stop watch.

STOP

Experiment on echoes


How can you use this result to estimate the speed of sound?

The sound of the starting pistol takes 0.92 s to travel a distance of 300 m.

=326 m/s

distancetime

speed =

= 3000.92

Repeat the experiment several times to obtain an average.

How does your calculation for the average speed of sound compare with the real speed?

Experiment on echoes


Echoes and reflection

What do we call reflected sound? an echo

Are hard or soft surfaces best at reflecting sound?

How are echoes reduced in cinemas and theatres?

By using soft materials on the walls such as curtains.

Name two animals that use echoes for navigation or communication.bats and dolphins

Hard surfaces produce strong echoes.


Waves: Sound

Contents

What is sound?


Hearing sound

Ultrasound



Sound waves can be studied with this type of equipment.

loudspeaker

signal generator

oscilloscope

Which piece of equipment…

• produces signals over a range of frequencies and of varying amplitudes?

• converts signals into sound waves?

• is used to study the frequency and loudness of a sound?

signal generator

oscilloscope

loudspeaker

Studying sound waves


loud soundquiet sound

What is the difference between the sound wave of a quiet sound and a loud sound?

The loud sound has taller waves.

What would the sound wave of a very loud sound look like?

The louder the sound, the greater the amplitude.

Why sound is quiet or loud?


Which is the loudest?

Sound A is the loudest.

Which trace represents the loudest sound?

Sound A has the largest amplitude, which means the wave has more energy and so the sound is louder.

A B


low pitch sound high pitch sound

What is the difference between the sound wave of a low pitch sound and a high pitch sound?

The high pitch sound has a shorter wavelength, so more waves are visible. It has higher frequency waves.

What would the sound wave of a very low sound look like?

Why sound is low pitch or high pitch?


Which is the highest?

Which trace represents the sound with the highest pitch?

Sound B is the highest pitched.

Sound B has the shortest wavelength and the most number of waves visible, so it has the highest frequency.

BA


Wave animation


Waves: Sound

Contents

What is sound?

Hearing sound

Ultrasound




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 these into electrical signals.

6.The auditory nerve takes the signals

to the brain.

3

4

5

61

2

How does the ear hear?


How does the ear hear?


Set the volume and increase the frequency of the signal provided by the signal generator.

20 Hz to 20 000 Hz

Humans cannot hear sounds of every frequency.

What is the hearing range of a healthy young person?

The range of frequencies you can hear is called your hearing range.

Can we hear all frequencies?


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 after which hearing recovers.

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

Does everyone have the same hearing range?

People lose the ability to hear sounds of high frequency as they get older.

Which end of their hearing range will be affected?

Do we have the same hearing?


100 000

10 000

1 000

100

10

1

0human dog elephantbat mouse dolphin

Do all animals have the same hearing range?

frequency(Hz)

Comparing hearing ranges


The loudness of a sound is measured in decibels (dB).

0 dB = quietest audible sound (near total silence)

10 dB = 10 times more powerful than the quietest sound

20 dB = 100 times more powerful than the quietest sound

1000 times

1000 times

How much more powerful than the quietest sound is 30 dB?

A whisper is 30 dB and normal conversation is 60 dB.

How much more powerful is normal conversation compared to a whisper?

How is loudness measured?


Any sound above 85 dB can damage hearing. You know you are listening to 85 dB sound if you have to raise your voice to be heard.

The amount of time spent listening to a loud sound also causes hearing problems.

Any 140 dB sound causes pain and immediate damage!

More than two hours of 100 dB sound can damage your ears.

What might also influence hearing loss?

Why are there laws about the maximum levels of sound that people should be exposed to at work?

When is sound dangerous?


What is noise?

A noise is any unwanted sound.

What one person considers noise another person might not. Can you name any examples?

List three effects of noise.

nauseaheadaches

deafness

List three ways of reducing the effects of loud noise.

ear protectors

putting noisy machinery in insulated roomsdouble glazing


160

140

120

100

80

60

40

20

0

permanent ear damage

can just be heard

aircraft overhead

decibels

circular saw at 2m

quiet countryside

pin being dropped

loud bell

personal stereo

How loud is loud?


The results of a hearing tested are shown on an audiogram.

It records the softest sound heard at each pitch .

The audiogram shows hearing sensitivity for different frequencies (pitch) at different intensities (volume).

frequency of sound (Hz)

inte

nsity

of s

ound

(dB

)

loud sound

moderate sound

soft sound

low pitch high pitch

How is hearing tested?


Which audiogram trace represents optimal hearing and which represents impaired hearing?

optimalhearing

impairedhearing

frequency of sound (Hz)

inte

nsity

of s

ound

(dB

)

Testing hearing


Waves: Sound

Contents

What is sound?

Hearing sound

Ultrasound




The upper frequency limit of human hearing 20 000 Hz.Any high frequency sound above 20 kHz is called…

Whales and dolphins communicate using ultrasound.

Why does a dog whistle vibrate at ultrasound frequencies?

Can you name another human use of ultrasound?

ultrasound

What is ultrasound?


dolphins

ultrasonic toothbrushjewellery cleaning

imaging fetuses

submarines

viewing kidney stones

echo location

batsultrasonic cleaning

Which of the following does not use ultrasound?

It’s a trick question! All of the above involve ultrasound.High frequencies can be very useful!

Using ultrasound


X rays are more energetic and penetrating and are a lot more dangerous, they could cause damage to the growing baby.

fetus at 10 weeks fetus at 20 weeksWhy is ultrasound for scanning fetuses instead of X rays which would give a clearer picture?

Ultrasound is the name given to a medical technique. It uses high frequency sound waves to produce images of inside the body without opening up the body.

Using ultrasound in medicine


Ultrasound, like all sound, is reflected when it meets different boundaries. So how is this used for imaging?

An ultrasound machine transmits high-frequency sound waves into the body.

These sound waves are reflected different amounts by different tissues.

The reflected waves are detected by a receiver. A computer turns the distance and intensities of these echoes into a two-dimensional image.

How does ultrasound imaging work?


Sound multiple choice

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