Sound Waves

Question 1

what are sound waves caused by?

Answer 1

vibracting objects

The vibrations are passed through the surrounding medium as a series of compressions.

Question 2

are sound waves transverse waves or longitudinal waves?

Answer 2

longitudinal waves

Question 3

how do you hear sound?

Answer 3

vibrations reach your eardums

Question 4

at what frequency is the human ear capable of hearing sounds

Answer 4

20 Hz and 20,000 Hz

Question 5

does sound travel faster in dense medium?

Answer 5

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.

Question 6

does sound waes reflect on hard surfaces

Answer 6

yes

Sound waves will be reflected by hard flat surfaces.

Question 7

how does sound waves behave with things like carpet and curtains?

Answer 7

Things like carpets and curtains act as absorbing surfaces, which will absorb sounds rather than reflect them.

Question 8

do sound waves retract (change direction ) as they enter different media?

Answer 8

yes , Sound waves will also refract (change direction) as they enter different media. As they enter denser material, they speed up.

Question 9

Describe the properties of sound waves

Answer 9

• Longitudinal waves
• Transfer energy
• Can be reflected, refracted and diffracted

Question 10

What is the the range of human hearing?

Answer 10

• 20 Hz - 20,000Hz

Question 11

How are pitch and frequency related?

Answer 11

• The higher the pitch, the higher the frequency of a sound wave

Question 12

How are loudness and amplitude related?

Answer 12

• The louder the sound, the higher the amplitude

Question 13

What is an oscilloscope?

Answer 13

• A machine used to view sound waves

Question 14

what is a oscilloscope?

Answer 14

An oscilloscope is a device which can display the microphone signal as a trace on a screen.

Question 15

what is a sound wave receiver?

Answer 15

A sound wave receiver, such as a microphone, can pick up sound waves travelling through the air.

Question 16

how do you display and measure sound waves properties?

Answer 16

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.

Question 17

on a oscilloscope what does the apperence of a wave show?

Answer 17

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.

Question 18

does loudness increase with amplitude?

Answer 18

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.

Question 19

does higher frequency result in higher pitch?

Answer 19

yes

Question 20

how is frequecy measured?

Answer 20

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).

Question 21

can you compare the frequency of waves on an oscilloscope?

Answer 21

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).

Question 22

if the source of sound vibrates with a high frequency, is the sound high pitched?

Answer 22

yes

e.g squeaking mouse

Question 23

if the source of sound vibrates with a low frequency, is the sound low pitched?

Answer 23

yes

e.g a mooing cow

Question 24

practical experiment

how do you use an oscilloscope to find frequency of a sound wave

Answer 24

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.

Question 25

**_tips_** Frequency is measured in hertz (Hz)

Answer 25

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.

Question 26

can you use oscilloscope to measure speed of sound

Answer 26

yes

Question 27

**_practical experiment_** how can you use an oscilloscope to measure the speed of sound?

Answer 27

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.

Question 28

**_TIP_** You can measure the speed of sound in other ways...

Answer 28

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.