Sound Waves Flashcards
what are sound waves caused by?
vibracting objects
The vibrations are passed through the surrounding medium as a series of compressions.
are sound waves transverse waves or longitudinal waves?
longitudinal waves
how do you hear sound?
vibrations reach your eardums
at what frequency is the human ear capable of hearing sounds
20 Hz and 20,000 Hz
does sound travel faster in dense medium?
yes,
Because sound waves are caused by vibrating particles, in general the denser the medium, the faster sound travels through it. This also means it can’t travel through a vacuum, where there aren’t any particles.
Sound generally travels faster in solids than in liquids, and faster in liquids than in gases.
does sound waes reflect on hard surfaces
yes
Sound waves will be reflected by hard flat surfaces.
how does sound waves behave with things like carpet and curtains?
Things like carpets and curtains act as absorbing surfaces, which will absorb sounds rather than reflect them.
do sound waves retract (change direction ) as they enter different media?
yes , Sound waves will also refract (change direction) as they enter different media. As they enter denser material, they speed up.
Describe the properties of sound waves
- Longitudinal waves
- Transfer energy
- Can be reflected, refracted and diffracted
What is the the range of human hearing?
- 20 Hz - 20,000Hz
How are pitch and frequency related?
- The higher the pitch, the higher the frequency of a sound wave
How are loudness and amplitude related?
- The louder the sound, the higher the amplitude
What is an oscilloscope?
- A machine used to view sound waves
what is a oscilloscope?
An oscilloscope is a device which can display the microphone signal as a trace on a screen.
what is a sound wave receiver?
A sound wave receiver, such as a microphone, can pick up sound waves travelling through the air.
how do you display and measure sound waves properties?
To display these sound waves, and measure their properties, you can plug the microphone into an oscilloscope. The microphone converts the sound waves to electrical signals.
on a oscilloscope what does the apperence of a wave show?
The appearance of the wave on the screen tells you whether the sound is loud or quiet, and high- or low-pitched. You can even take detailed measurements to calculate the frequency of the sound (see next page) by adjusting the settings of the display.
does loudness increase with amplitude?
yes
The greater the amplitude of a wave, the more energy it carries. In sound this means it’ll be louder. Louder sound waves will also have a trace with a larger amplitude on an oscilloscope.
does higher frequency result in higher pitch?
yes
how is frequecy measured?
Frequency is the number of complete vibrations each second, and it’s measured in hertz (Hz) — 1 Hz is equal to 1 vibration per second. Other common units are kHz (1000 Hz) and MHz (1 000 000 Hz).
can you compare the frequency of waves on an oscilloscope?
yes
You can compare the frequency of waves on an oscilloscope — the more complete cycles displayed on the screen, the higher the frequency (if the waves are being compared on the same scale — see below).
if the source of sound vibrates with a high frequency, is the sound high pitched?
yes
e.g squeaking mouse
if the source of sound vibrates with a low frequency, is the sound low pitched?
yes
e.g a mooing cow
practical experiment
how do you use an oscilloscope to find frequency of a sound wave
1) The horizontal axis on the oscilloscope display is time.
2) The time between each division on the scale can be adjusted to get a clear, readable trace. Here, each division has been set to show 0.00001 s.
3) Adjust the time division setting until the display shows at least 1 complete cycle, like this.
4) Read off the period — the time taken for one complete cycle.
Here 1 cycle crosses 20 divisions, so
period = 20 × 0.00001 s = 0.0002 s.
Frequency = 1 ÷ period (see page 51)
= 1 ÷ 0.0002 s = 5000 Hz = 5 kHz.
tips
Frequency is measured in hertz (Hz)
Remember: if the waves on the oscilloscope get closer together, the frequency has increased and the sound will be higher pitched. If they get taller, the amplitude has increased and the sound will be louder.
can you use oscilloscope to measure speed of sound
yes
practical experiment
how can you use an oscilloscope to measure the speed of sound?
1) By attaching a signal generator to a speaker you can generate sounds with a specific frequency. You can use two microphones and an oscilloscope to find the wavelength of the sound waves generated:
2) The detected waves at each microphone can be seen as a separate wave on the oscilloscope.
3) Start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display, but exactly one wavelength apart.
4) Measure the distance between the microphones to find the wavelength (lambda symbol ).
5) You can then use the formula v = f × lambda symbol (see page 51) to find the speed (v) of the sound waves passing through the air — the frequency (f) is whatever you set the signal generator to in the first place.
6) The speed of sound in air is around 340 m/s, so check your results roughly agree with this.
TIP
You can measure the speed of sound in other ways…
For example, you can ask a friend to stand a long distance away (e.g. 100 m) and bang a drum (or do something else that makes a loud bang). You can use a stopwatch to measure the time taken between you seeing the person make the noise, and when you hear it. Then use “speed = distance ÷ time” (see page 1) to work out the speed of the sound waves.
