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IGCSE Physics Revision > Sound > Flashcards

Sound Flashcards

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1
Q

What are sound waves?

A

Sound waves are longitudinal waves

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2
Q

What can be done to sound waves?

A

They can be reflected, refracted and diffracted

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3
Q

How are sound waves produced?

A

by objects vibrating

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4
Q

How do we hear sounds?

A

These vibrations (compressions and rarefactions) of air particles reach our ears and cause the eardrum to vibrate. The vibrations are converted to electrical signal which are detected by the brain.

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5
Q

How does a speaker cone create a sound?

A

As the cone moves L and R it pushes air molecules close together; COMPRESSION.

These particles push against neighbouring particles so that the compression appears to be moving right.

Behind the compression is a region where the particles are spread out; RAREFACTION.

By vibrating several times the cone has created a series of compressions and rarefactions travelling away from it. A LONGITUDINAL SOUND WAVE.

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6
Q

What can sound waves travel through best?

A

solids because there are more particles closer together to transmit the sound wave more quickly

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7
Q

Why can sound waves not travel in a vacuum?

A

there are no particles to carry the vibrations

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8
Q

Experiment to show that sound doesn’t travel in a vacuum?

A

Put a bell in a jar and ring it. We can see and hear the bell therefore light and sound travel in air. But when air is removed we can only see the bell so sound doesn’t travel in a vacuum.

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9
Q

Why is sound energy transferred much faster in liquids and solids?

A

the particles are much closer together meaning it is easier to transfer sound energy and more QUICKLY

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10
Q

How to measure speed of sound with echoes?

A
  1. Stand 50m from a wall and clap your hands 20 times
  2. An echo will be heard soon after each clap.
  3. Time how long it takes for 20 echoes to be heard.
  4. The sound altogether travelled 100m there and back 20 times
  5. The speed is 2000 x the time measured!
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11
Q

How to measure sound speed with resonance tube?

A
  1. Tuning fork produces vibrations and known frequency
  2. The sound wave is reflected at the water boundary
  3. If the tube is the right length (1/4 wavelength) the reflected wave will reinforce the original one giving a large amplitude and louder sound that can be heard.

RESONANCE

  1. The first resonance is heard when the length of the air in the tube is 1/4 wavelength. When the sound is heard the length of air tube is measured and multiplied by 4 to get the full wavelength.
  2. v = f x l
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12
Q

How to measure the speed of sound with an oscilloscope?

A
  1. Set up simple generator, two microphones and an oscilloscope
  2. Set generator to give sound of frequency 1 kHz
  3. Start microphones close together and move apart until they are a complete wavelength away (trace on oscilloscope are exactly one above the other)
  4. Measure the distance between the two microphones
  5. Frequency can be found from the oscilloscope by doing 1/T
  6. Speed is calculated by v = f x l
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13
Q

What is a reflected sound wave?

A

an echo

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14
Q

What is special when a sound waves strikes a surface?

A

the angle of incidence = angle of reflection

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15
Q

How does SONAR work?

A

Sound waved are emitted from the ship and travel to the seabed.

Equipment on the ship detects some of the sound waves that are reflected by the seabed.

The depth of the seabed can be calculated from the time between sending the sound wave and detecting the echo.

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16
Q

If fish are below the ship the reflected sound wave is distorted. Why are there two pulses of lower amplitude than the original?

A

The fish and seabed pulses have smaller amplitudes than the original because…

Not all of the pulse is reflected by the fish or the seabed.

Some ultrasound will be absorbed by the fish/water/seabed

Some ultrasound will be scattered and not return to the boat

Because reflection is taking place at different depths in the shed the sharp pulse becomes longer when it returns to the boat.

17
Q

When is there optimum diffraction?

A

When the gap is near to the wavelength

18
Q

What is a high pitch?

A

When the thing producing the sound vibrates quickly and so, produces sound waves with a high frequency.

19
Q

What is a low pitch?

A

When the thing producing the sound vibrates slowly and so, produces sound waves with a low frequency.

20
Q

What is frequency?

A

number of waves/second

21
Q

What is frequency measured in?

A

Hz

22
Q

What do the peaks and troughs represent on the CRO for sound waves?

A 
peak = compression
trough = rarefaction
23
Q

What is the audible range for humans?

A

20Hz to 20000 Hz

24
Q

What is sound above and below the audible range?

A

ultrasound and infrasound

25
Q

How is something shown to be loud on the CRO?

A

High amplitude

26
Q

How is something shown to be quiet on the CRO?

A

Small amplitude

27
Q

How is something made loud?

A

If the strings are struck hard lots of energy is transferred to them from whatever it has been struck with. The moves the particles even more from their equilibrium position and so we interpret the sound as louder.

Here the sound waves are transferring more energy.

28
Q

How is something made quiet?

A

If it is struck gently the compressions created are less dense and less energy is transferred by the sound waves

29
Q

What is ultrasound?

A

The frequency is above the human range (20,000 Hz)

30
Q

What are medical uses of ultrasound?

A

pre-natal scanning
removal of kidney/gall stones
repair of damaged muscle/tissue
removing plaque from teeth

31
Q

Describe the differences between ultrasound waves emitted by the transducer and those detected back at it

A

Reflected Waves:

lower frequency
longer wavelength
less intensity (amplitude decreased)
32
Q

Describe the features of X rays and what happens when they enter the body

A

Description of an X-ray

X-rays are electromagnetic waves / part of the electromagnetic spectrum

X-rays are (very) high frequency (waves) through a vacuum at the speed of light

X-rays are (very) high energy (waves)

X-rays have a (very) short wavelength

Wavelength (of X-rays) is of a similar size to (the diameter of) an atom

X-rays are a transverse wave - oscillations / vibrations are
perpendicular to direction of energy transfer

X-rays are ionising radiation

Statement(s) as to what happens to X-rays inside the human body:

X-rays are absorbed by bone
X-rays travel through / are transmitted by tissue / skin

33
Q

Describe the features of ultrasound and what happens when it enters the body

A

Description of ultrasound

ultrasound has a frequency above 20 000 (hertz) so therefore beyond the human (upper) limit (of hearing)

ultrasound is a longitudinal wave – oscillations / vibrations (of
particles) are parallel to direction of energy transfer

Statement as to what happens to ultrasound inside body:

ultrasound is (partially) reflected at / when it meets a boundary between two different media

travel at different speeds through different media

Statement as to what happens to ultrasound inside body:

ultrasound is (partially) reflected at / when it meets a boundary between two different media

travel at different speeds through different media

34
Q

Why are X rays dangerous to use for prenatal scanning?

A

Ionizing

Damage cells/DNA/chromosome and nucleus

Cause mutations

Kill cells

Produce abnormal growth and so make cells cancerous

35
Q

Why can astronauts not hear from outside their space suits?

A

Sound cannot travel through a vacuum as there is no medium in which vibrations can be set up and no particles to vibrate

36
Q

Why does sound reflected at a boundary decrease when metal is changed to glass?

A

Less sound is reflected

Some sound is absorbed by/passes through glass

IGCSE Physics Revision (6 decks)

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