Ch12 Sound

Question 1

Why are sound waves sometimes referred to as pressure waves?

Answer 1

The vibrations of the sound source cause a regular variation in the pressure of the medium.

Question 2

What is the audible range of frequencies for humans?

Answer 2

Between 20 and 20 000 hertz

Question 3

Why can’t sound waves propagate through a vacuum?

Answer 3

Sound is a mechanical wave, which means it need a medium to travel (propagate) through. A vacuum is an empty space with no particles so it isn’t possible for sounds to travel through because there are no particles to carry the vibrations.

Question 4

Define compressions:

Answer 4

A region of a sound wave where the particles are pushed together
Regions of high pressure

Question 5

Define rarefactions:

Answer 5

A region of a sound wave where the particles are further apart
Regions of low pressure

Question 6

Define amplitude:

Answer 6

The biggest height/depth of a wave from its undisturbed position

Question 7

Define frequency:

Answer 7

The number of complete vibrations/waves per unit time

Question 8

Define hertz:

Answer 8

The unit o frequency
1Hz = 1 wave per second

Question 9

Define ultrasound:

Answer 9

Any sound with a frequency higher than 20 000 Hz

Question 10

Why are sound waves longitudinal?

Answer 10

The vibrations create compressions and rarefractions which creates pressure changes
The air particles vibrate parallel to the direction of propagation.

Question 11

What are 3 factors affections the speed of sound?

Answer 11

1) density of the medium
2) temperature of the medium
3) pressure of the medium

Question 12

Why do sound waves travel faster through solids than liquids or gasses?

Answer 12

Denser mediums → sound waves → travel more quickly → their particles are closer together

Question 13

Why do sound waves travel faster through a medium with a higher temperature?

Answer 13

The higher the temp of medium → faster the particles move → more kinetic energy → quicker sound can travel through the medium faster

Question 14

How does pressure influence the speed of sound waves?

Answer 14

The more pressure in medium → closer particles are in medium → faster sound can travel through

Question 15

Define echo:

Answer 15

Echoes are reflected sounds from surrounding objects

Question 16

What is a similarity and difference between the echo and the original sound?

Answer 16

They have the same characteristics but travel in opposite directions

Question 17

What does sonar stand for?

Answer 17

Sound Navigation And Ranging

Question 18

Define echolocation:

Answer 18

A technique used by some animals to detect the location of their surrounding obstacles by using reflected sound

Question 19

What are the shapes of waves called?

Answer 19

Waveforms

Question 20

What does an oscilloscope do?

Answer 20

It is a voltmeter that changes electrical signals into visual traces on the screen
The visual trace is actually a graph of voltage against time

Question 21

Define the period(T) of a wave:

Answer 21

The length of time that it takes for one complete cycle (wave) to pass a fixed point

Question 22

What is the symbol for frequency?

Answer 22

f

Question 23

Define frequency:

Answer 23

The number of complete cycles (waves) passing a fixed point per second

Question 24

What is the equation for frequency?

Answer 24

f=1/T

Question 25

What is the **equation** for the period of a wave?

Answer 25

T=1/f

Question 26

What is the unit for frequency?

Answer 26

hertz (Hz)

Question 27

What does the amplitude of a sound wave determine?

Answer 27

The **Volume**/**Loudness**

Question 28

What does a bigger amplitude mean:

Answer 28

Louder sound

Question 29

What does a smaller amplitude mean:

Answer 29

Softer sound

Question 30

What does the volume of a sound depend on?

Answer 30

1) Amplitude of a sound wave 2) Whether its frequency lies in a region where the ear is more/less sensitive

Question 31

What does the frequency of a wave determine?

Answer 31

The pitch

Question 32

What does a higher frequency mean?

Answer 32

A higher pitch

Question 33

What does a lower frequency mean?

Answer 33

A lower pitch

Question 34

Define **infrasound**:

Answer 34

Sounds w a frequency lower than 20Hz

Question 35

Define **ultrasound**:

Answer 35

Sounds with a frequency higher than 20 000Hz

Question 36

What animals use **infrasound** to communicate?

Answer 36

Whales Alligators

Question 37

What animals use **ultrasound** for echolocation?

Answer 37

Dolphins Bats

Question 38

How does ultrasound to form images work?

Answer 38

When ultrasound is sent through the body and it reaches the boundary between 2 different mediums (difference in substance like bodily fluid and muscle) part of the wave is transmitted through the next medium and another part is reflected. The reflected waves are detected and electronically combined to form an image of the region

Question 39

What are the benefits of using ultrasound in medicine?

Answer 39

It is a safe and non-invasive way of scanning the body

Question 40

What are 2 characteristics of ultrasound waves:

Answer 40

1) High frequency 2) Very short wavelengths

Question 41

Define a longitudinal wave:

Answer 41

The direction of the disturbance, that is the direction in which the particles in the medium vibrate, is **parallel** to the direction of propagation of the wave.

Question 42

How would you calculate how far away a storm is?

Answer 42

Find the time between the lightning and thunder and devide by 3. → sound travels 1km in about 3 seconds

Question 43

What is the speed of sound in air?

Answer 43

Between 330 m/s and 350 m/s

Question 44

Why is there barely an echo in a classroom but outside might be more of an echo?

Answer 44

In a classroom the objects that the sound reflect of are nearby so the echo will be so close to the original sound, you wont even hear it. Outside the sound has to travel a lot further so you may hear an echo

Question 45

Define wavelength:

Answer 45

The distance between 2 successive points that are exactly in phase Ex. Between 2 successive troughs/crests

Question 46

Define pulse:

Answer 46

A single disturbance that is propagated from one point to another in a medium

Question 47

Define medium:

Answer 47

A substance through which a disturbance travels

Question 48

Define propagate:

Answer 48

Process by which a disturbance travels through a medium

Question 49

Define equilibrium position:

Answer 49

Rest position of the medium where there is no disturbance

Question 50

Define superposition:

Answer 50

Superposition of waves is the **addition** of the disturbances (amplitudes) of the 2 pulses that occupy the same space at the same time

Question 51

Define interference:

Answer 51

When 2/more pulses/waves move through the same space at the same time, as they overlap the phenomena of interference can be observed

Question 52

What are the 2 types of interference?

Answer 52

1) constructive interference 2) destructive interference

Question 53

Define constructive interference:

Answer 53

When **2 pulses amplify** each other to result in a **single pulse** with a **greater amplitude**

Question 54

Define destructive interference:

Answer 54

When 2 pulses **weaken/cancel**each other and result in a **single pulse** with a **smaller amplitude/no pulse**