© Boardworks Ltd 2004 Using Sound KS4 Physics. Learning Objectives Understand how sound is heard and the audible frequencies of human hearing Understand.

© Boardworks Ltd 2004

Using Sound

KS4 Physics

Learning Objectives• Understand how sound is heard and the

audible frequencies of human hearing• Understand how the loudness of sound is

quantified, and what is meant by “noise”• Understand the nature and uses of

ultrasound.

• Textbook references: 6.06 (p. 134-135)• 6.10 (p. 142-143)

Different speeds of sound

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

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

Breaking the sound barrier!

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?

Reflected sound waves

Echoes and reflection

What do we call reflected sound?

Are hard or soft surfaces best at reflecting sound?

How are echoes reduced in cinemas and theatres?

Name two animals that use echoes for navigation or communication.

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

6

1

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.

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

0

human 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

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.

List three ways of reducing the effects of loud noise.

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 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 toothbrush

jewellery cleaning

imaging fetuses

submarines

viewing kidney stones

echo location

bats

ultrasonic 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

Learning Objectives• Understand how sound is heard and the

audible frequencies of human hearing• Understand how the loudness of sound is

quantified, and what is meant by “noise”• Understand the nature and uses of

ultrasound.

• Textbook references: 6.06 (p. 134-135)• 6.10 (p. 142-143)