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AQA GCSE 3-2B Sound . GCSE Physics pages 244 to 251. July 26 th 2011. SOUND 13.5 What is sound? Using skills, knowledge and understanding of how science works: • to compare the amplitudes and frequencies of sounds from diagrams of oscilloscope traces.

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aqa gcse 3 2b sound

AQA GCSE 3-2BSound

GCSE Physics pages 244 to 251

July 26th 2011

aqa gcse specification
SOUND

13.5 What is sound?

Using skills, knowledge and understanding of how science works:

• to compare the amplitudes and frequencies of sounds from diagrams of oscilloscope traces.

Skills, knowledge and understanding of how science works set in the context of:

• Sound is caused by mechanical vibrations and travels as a wave.

• Sounds in the range 20-20 000 Hz can be detected by the human ear.

• Sound cannot travel through a vacuum.

• The pitch of a note increases as the frequency increases.

• The loudness of a note increases as the amplitude of the wave increases.

• The quality of a note depends upon the waveform.

• Sound waves can be reflected and refracted.

ULTRASOUND

13.6 What is ultrasound and how can it be used?

Using skills, knowledge and understanding of how science works:

• to compare the amplitudes and frequencies of ultrasounds from diagrams of oscilloscope traces

• to determine the distance between interfaces in

Skills, knowledge and understanding of how science works set in the context of:

• Electronic systems can be used to produce ultrasound waves which have a frequency higher than the upper limit of hearing for humans.

• Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector is a measure of how far away such a boundary is.

• Ultrasound waves can be used in industry for cleaning and quality control.

• Ultrasound waves can be used in medicine for pre-natal scanning.

AQA GCSE Specification
sound
Sound is produced by vibrating objects.

A sound wave consists of mechanical vibrations in air and other substances.

Sound is a longitudinal wave in which the wave energy travels in the same direction as the particles within the wave vibrate.

Most other types of wave are transverse. For example water and light waves. In these cases the particles making up the wave vibrate at ninety degrees to the direction of energy transfer.

vibrations

wave direction

vibrations

wave direction

Sound

LONGITUDINAL WAVE

TRANSVERSE WAVE

slide4
Through air a sound wave consists of a series of compressions and rarefactions.

A compression is a region of slightly higher pressure where the air molecules are closer together than usual.

A rarefaction is the opposite.

compression

loudspeaker

no sound wave

sound wave

rarefaction

wavelength

speed of sound
Speed of sound

330

342

1 500

5 000

Sound does not travel through a vacuum.

In space no one can hear you scream!

– tagline of the film Alien (1979)

question
A thunderclap is heard 12 seconds after a lightning flash. Calculate the distance to the lightning flash.

Take the speed of sound = 340 m/s

speed = distance / time

becomes: distance = speed x time

= 340 m/s x 12 seconds

= 4 080 m

Distance = 4.08 km

Question
bell jar experiment
Bell jar experiment

This experiment shows that sound needs a material medium for transmission.

As the air pressure inside the bell jar is reduced the loudness of the sound heard outside decreases.

The bell can be still seen to be working normally.

range of hearing
Range of hearing

Humans can hear sounds in the range 20 Hz to 20 000 Hz.

Age and damage reduces the upper limit.

For example an old person or someone exposed to prolonged high sound volume may no be able to hear above 10 000 Hz.

Some animals can hear much higher frequencies:

dogs – 40 000 to 60 000 Hz (depends on the breed)

bats and dolphins – 100 000 Hz

reflection of sound
Question:

A misguided child shouts ‘Chelsea!’ at a nearby cliff and hears their echo 1.4 s later. How far away is the cliff?

Take the speed of sound = 340 m/s.

distance, D

Reflection of sound

An echo is a reflected sound wave.

The sound travels to and from the cliff, a total distance of 2D

speed = distance / time

becomes: distance = speed x time

= 340 m/s x 1.4 s

= 476 m

= 2D !

Therefore distance to the cliff = 238 m.

sound refraction

C

A

B

cooler air

Sound refraction

The sound produced by person A may be heard more clearly by person B than by person C.

The cooler air over the water refracts the sound waves downwards.

sound notes questions from pages 244 245
(a) What type of objects produce sound waves? (b) What is the typical range of frequencies audible to a young person? (c) How does this range change with age?

Draw a diagram and describe an experiment to show that sound waves do not travel through a vacuum.

Draw Figure 1 on page 244 and explain the difference between longitudinal and transverse waves. State which type is sound.

(a) What is an echo? (b) How are echoes affected by the surface of materials?

Why does sound travel better at night?

Copy and answer questions (a), (b), (c), (d) and (e) on pages 244 and 245.

Copy the ‘Key points’ table on page 245.

Answer the summary questions on page 245.

Sound Notes questions from pages 244 & 245
sound answers
In text questions:

A mouse.

The sound becoming audible again.

Wave one end from side to side.

There are no reflections, so each note dies away more quickly outdoors.

Colder.

Summary questions:

(a) Reflected.

(b) Scattered, absorbed.

(c) Refracted.

2. (a) About 18000 Hz

(b) The vibrating surface of the loudspeaker pushes the air near it to and fro, creating sound waves which spread out from the loudspeaker.

(c) The ball inside goes around at constant speed and makes the surrounding air vibrate.

Sound ANSWERS
sound waves on oscilloscopes
An oscilloscope is a device that can be used to display a sound wave.

The screen displays a graph of how the amplitude of the sound wave varies with time.

Sound waves on oscilloscopes
pitch
The pitch of a musical note increases with frequency.

low pitch

high pitch

Pitch

Examples:

Concert pitch A = 440 Hz; Top C = 523 Hz

Doubling the frequency increases the pitch by one octave. Therefore the ‘A’ above top C will have frequency 880 Hz.

quality
The quality or timbre of a musical note is what makes one musical instrument sound different from another.

Despite different instruments producing a note of the same loudness and pitch, the shape of the wave will be different.

Quality
question17
The diagram opposite shows the appearance of a sound wave on an oscilloscope. Draw a second diagram showing the appearance of a sound wave of lower pitch but greater loudness.Question
question18
Question

Choose appropriate words to fill in the gaps below:

Sound is a ___________ wave that in air consists of a series of compressions and _____________.

Sound travels fastest through _______ but does not travel at all through a __________.

A ____________ sound wave is called an echo. Sound also undergoes ___________.

The loudness of a sound increases with wave __________, the pitch with wave ____________.

longitudinal

rarefactions

solids

vacuum

reflected

refraction

amplitude

frequency

WORD SELECTION:

solids

rarefactions

refraction

vacuum

amplitude

longitudinal

reflected

frequency

musical sounds notes questions from pages 246 247
Explain the difference between a musical note and noise.

Draw wave diagrams to explain what happens when there is an increase in a sound wave’s (a) loudness and (b) pitch.

Copy and answer questions (a), (b) and (c) on pages 246 and 247.

Explain how the three main categories of musical instrument produce sound.

Why do different musical instruments producing the same note sound different from each other? Illustrate your answer with a waveform diagram.

Copy the ‘Key points’ table on page 247.

Answer the summary questions on page 247.

Musical sounds Notes questions from pages 246 & 247
musical sounds answers
In text questions:

An ambulance, a police vehicle, a fire engine, an ice cream van.

The waves are not as tall.

The waves would be smaller in height and stretched out more.

Summary questions:

1. (a) The waves would be taller but would have the same spacing.

(b) The waves would be more stretched out but would have the same height.

2. (a) (i) The note has a higher pitch (frequency).

(ii) The note has a higher pitch (frequency).

(b) The sound of a violin (played correctly) lasts as long as the violin bow is in contact with a string. The sound of a drum dies away after the drum skin has been struck. A drum note is less rhythmical than a violin note.

Musical sounds ANSWERS
ultrasound
Ultrasound is very high frequency sound that is above 20 000 Hz, too high to be heard by humans.

Some animals, for example dogs, bats and dolphins can communicate or navigate using ultrasound.

Ultrasound echoes can be used to measure distance (e.g. sonar) and to see inside objects (scans).

Ultrasound
ultrasound scans
Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector is a measure of how far away such a boundary is.

Ultrasound reflects off each tissue boundary

Developing baby

Ultrasound transmitter

Ultrasound scans
2 quality control
2. Quality control

Ultrasonic testing is a type of non-destructive testing commonly used to find flaws in materials and to measure the thickness of objects.

At a construction site, a technician tests a pipeline weld for defects using an ultrasonic instrument.

question26
The oscilloscope trace opposite was obtained from the scan of a metal block.

(a) how many flaws are present according to this display?

(b) If the width of the block was 300 mm calculate the distance fro the front of the block to each flaw.

There are two flaws.

(b) The width of the block is represented by 8.3 squares.

Therefore each square represents 300mm / 8.3

= 36.1 mm per square

The two flaws occur after 3.0 and 4.2 squares

Therefore:

1st flaw is at 3.0 x 36.1

= 108 mm from the front

2nd flaw is at 4.2 x 36.1

= 152 mm from the front

Question
ultrasound cleaning

Another way of cleaning teeth

Jewellery immersed in water

Ultrasound cleaning

The very high frequency waves of ultrasound can be used to shake off dirt or grease.

question28
Question

Choose appropriate words to fill in the gaps below:

Ultrasound is very high ___________ sound. It is above the upper range of _________ hearing, more than 20 000 _______.

Ultrasound can be used to measure __________, for example SONAR.

Ultrasound can be used to obtain ________, for example of a developing _______ within a mother’s womb.

Ultrasound can also be used to _______ objects.

frequency

hertz

human

distance

scans

baby

clean

WORD SELECTION:

baby

human

scans

frequency

distance

clean

hertz

ultrasound notes questions from pages 248 249
What is ultrasound? State a frequency as part of your answer.

Copy and answer question (a) on page 248.

(a) Describe how ultrasound is used to obtain pre-natal scans. (b) What are the advantages of ultrasound scans over X-ray imaging?

How is ultrasound used in cleaning?

Draw the diagram shown in summary question 2 and explain how ultrasound can be used to detect flaws inside solid objects.

Copy and answer question (b) on page 249.

Copy the ‘Key points’ table on page 249.

Answer the summary questions on page 249.

Ultrasound Notes questions from pages 248 & 249
ultrasound answers
In text questions:

The material absorbs some of the ultrasonic sound from the loudspeaker.

They do not vibrate fast enough.

30 mm from the transmitter.

Summary questions:

1. (a) The organs have a different density to the surrounding tissue. So ultrasound is reflected at the tissue/organ boundaries.

(b) Ultrasound is not ionising radiation whereas X-rays are. Ionising radiation is harmful to living tissue. Ultrasound is reflected at the boundaries between different types of tissue, whereas X-rays are not.

2. (a) Two.

(b) 32-34 mm and 50 mm.

Ultrasound ANSWERS
sound simulations
Sound - PhET - This simulation lets you see sound waves. Adjust the frequency, volume, and harmonic content and you can see and hear how the wave changes. Move the listener around and hear what she hears

Vend diagram quiz comparing light and sound waves - eChalk

Ultrasound scanning - Explore Science

BBC KS3 Bitesize Revision:

KS3 Sound Contents Page

What is sound?

Loudness

Pitch

Hearing

Test bite on KS3 Sound

Sound Simulations
light and sound issues answers
(a) Air pollution due to dust particles, microbes in the air if hose equipment is not clean.

(a) To make sure the test is a fair comparison of the different materials.

(b) Cushion fabric is the best absorber, soft wallpaper is next and plaster board is next. wood panel reflects sound waves more than plaster board does.

Light and sound issuesANSWERS