3.4 Sound (Cambridge (CIE) O Level Physics): Flashcards
Exam code: 5054
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Define a longitudinal wave, using sound as an example.
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Cards in this collection (35)
Define a longitudinal wave, using sound as an example.
A longitudinal wave is one in which the vibrations occur in the same direction as the energy transfer. Sound waves are longitudinal.
Define compression and rarefaction.
A compression is a region of higher density, where molecules are bunched together. A rarefaction is a region of lower density, where molecules are spread out.
Why can sound waves not travel through a vacuum?
Sound waves are longitudinal waves, which require a medium to travel through. A vacuum contains no molecules, so there is no medium for the sound wave to travel through.
What is the range of frequencies audible to a healthy human ear?
20 Hz to 20 000 Hz
In the bell jar experiment, what happens to the sound of a ringing bell as the air is gradually pumped out?
The volume of the sound heard gradually decreases as the air is removed, until the ringing cannot be heard at all once the air is completely removed.
Sound is a type of ______ wave, because compressions and rarefactions cause changes that vary in time with the wave.
Sound is a type of pressure wave, because compressions and rarefactions cause changes that vary in time with the wave.
True or False?
Sound waves are transverse waves.
False.
Sound waves are longitudinal waves — the vibrations occur in the same direction as the energy transfer, not perpendicular to it.
Define pitch, in terms of a sound wave's frequency.
Pitch is related to the frequency of a sound wave. Sounds with a high pitch have a high frequency (short wavelength); sounds with a low pitch have a low frequency (long wavelength).
Define loudness (volume), in terms of a sound wave's amplitude.
Loudness (volume) is related to the amplitude of a sound wave. Sounds with a large amplitude have a high volume; sounds with a small amplitude have a low volume.
What is an oscilloscope used for?
An oscilloscope is a device used to study a rapidly changing signal, such as a sound wave or an alternating current, by displaying it on screen.
On an oscilloscope screen, how is a sound wave displayed, even though sound is a longitudinal wave?
The longitudinal sound wave is displayed as though it were a transverse wave.
On an oscilloscope trace of a sound wave, what do the height of the wave and the number of waves shown each represent?
The height (measured from the centre of the screen) represents the amplitude of the sound. The number of complete waves shown represents the frequency.
If the frequency of a sound wave ______, more waves are displayed on the oscilloscope screen.
If the frequency of a sound wave increases, more waves are displayed on the oscilloscope screen.
True or False?
A sound with a large amplitude has a low pitch.
False.
Amplitude relates to volume (loudness), not pitch — a large amplitude gives a high volume. Pitch is determined by frequency.
Define an echo.
An echo is the reflection of a sound wave off a hard surface.
What is echo sounding used for?
Echo sounding uses reflected sound waves to measure the depth of water or to detect objects underwater.
In echo sounding, why is the total distance travelled by the sound wave equal to twice the depth of the water?
The sound wave travels down from the surface to the ocean floor, then back up to the surface, so it covers the depth twice: once on the way down and once on the way back.
What three pieces of apparatus are used in the experiment to measure the speed of sound using echoes from a wall?
A trundle wheel (to measure the distance to the wall), two wooden blocks (to make a clap) and a stopwatch (to time from clap to echo).
In the echo experiment, the speed of sound is calculated using the equation v = ______ / t, where d is the distance to the wall.
In the echo experiment, the speed of sound is calculated using the equation v = 2*d / t, where d* is the distance to the wall.
True or False?
Sound waves reflect off soft surfaces to produce an echo.
False.
Sound waves reflect off hard surfaces to produce an echo.
What is the typical speed of sound in air at room temperature, and how does it change with temperature?
About 340 m/s (range 330–350 m/s). The speed of sound increases as the air temperature increases.
Rank the speed of sound in solids, liquids and gases from fastest to slowest, with typical values.
Solids (≈ 5000 m/s) > liquids (≈ 1500 m/s) > gases (≈ 350 m/s). Sound travels fastest in solids and slowest in gases.
Describe the apparatus and procedure for measuring the speed of sound directly between two points.
Two people stand about 100 m apart (distance measured with a trundle wheel). One bangs two wooden blocks together; the other starts a stopwatch on seeing this and stops it on hearing the sound. The test is repeated and averaged, then speed = distance / time.
Describe the apparatus and procedure for measuring the speed of sound using an oscilloscope.
Two microphones are placed about 5 m apart (measured with a tape measure) and connected to an oscilloscope. Two wooden blocks are clapped next to the first microphone; the oscilloscope shows the time difference between the sound arriving at each microphone, giving speed = distance between microphones / time between peaks.
Describe an experiment to measure the speed of a ripple on a water surface.
Two people stand a measured distance apart on a calm water surface (e.g. a lake), using a tape measure. One disturbs the surface to create a ripple; the other starts a stopwatch when the ripple is created and stops it when the ripple reaches them. This is repeated and averaged, then speed = distance moved / time taken.
Average speed of sound = distance moved / ______
Average speed of sound = distance moved / time taken
True or False?
Sound travels fastest through gases and slowest through solids.
False.
Sound travels fastest through solids and slowest through gases.
Define ultrasound.
Ultrasound is the name given to sound waves with a frequency greater than 20 000 Hz.
What is the normal range of human hearing?
About 20 Hz to 20 000 Hz, although this range decreases with age.
What happens to ultrasound waves when they reach a boundary between two different media?
Some of the waves are partially reflected at the boundary, while the remainder continue through and are transmitted.
Give three uses of ultrasound in medicine.
Constructing images of a foetus in the womb, generating 2D images of organs and internal structures not surrounded by bone, and as a treatment (e.g. removing kidney stones).
Why is ultrasound often preferred over other medical imaging techniques?
It is non-invasive and is believed to be harmless.
How is ultrasound used to detect a crack inside a metal object?
A crack causes some of the ultrasound waves to reflect earlier than the rest, producing an extra pulse on an oscilloscope trace. Since the wave speed is constant, the time between pulses can be used to calculate the distance to the crack.
An ultrasound transducer can both ______ and ______ ultrasound.
An ultrasound transducer can both emit and receive ultrasound.
True or False?
Ultrasound waves have a frequency lower than 20 000 Hz.
False.
Ultrasound waves have a frequency greater than 20 000 Hz.
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