Lecture 2

Question 1

What is the definition of oscillations

Answer 1

Movements or processes that, to one degree or another, repeat over time

Question 2

When are oscillations periodic

Answer 2

if: x(t) = x(t+nT)

Question 3

How is energy transferred in wave motion

Answer 3

Over a distance

Question 4

The two main types of waves

Answer 4

Mechanical waves
Electromagnetic waves

Question 5

Mechanical waves

Answer 5

-Some physical medium is being distributed
-The wave is the propagation of a disturbance through a medium

Question 6

Electromagnetic waves

Answer 6

-No medium required
-For example; light, radio waves and x-rays

Question 7

What is a wave/process?

Answer 7

The process of propagation of oscillations in a continuous medium

Question 8

One fundamental property of all waves

Answer 8

The transfer of energy without the transfer of matter

Question 9

What is the crest

Answer 9

The location of the maximum displacement of the element from its normal position

Question 10

What is the amplitude (A)

Answer 10

The distance between the resting position and maximum displacement

Question 11

What is the wavelength

Answer 11

The distance from one crest to the next crest

Question 12

What is the period (T)

Answer 12

The time interval required for two identical points of adjacent waves to pass by a point

Question 13

What is the frequency (v)

Answer 13

The number of crests (or any point on the wave) that pass a given point in a unit time interval

Question 14

Longitudinal waves

Answer 14

Mechanical waves in which the oscillations of the particles are in the direction of propagation of the wave

Question 15

Transverse waves

Answer 15

Waves in which the oscillations are in a direction perpendicular to the direction of propagation of the wave

Question 16

Which types of waves can propagate in liquids and solids

Answer 16

-Both longitudinal and transverse waves can propagate in a solid
-Only longitudinal waves can propagate in liquids

Question 17

Compression and rarefaction definitions

Answer 17

-An increase in pressure is compression
-Decrease in pressure is rarefaction

Question 18

What is sound

Answer 18

An elastic wave with a frequency in the range of 16-20,000Hz.

This is the hearing diapason of the human ear

Question 19

3 types of sound waves

Answer 19

-Audible waves
-Infrasonic waves
-Ultrasonic waves

Question 20

Audible waves

Answer 20

They are within the sensitivity of the human ear (20Hz-20kHz)

Question 21

Infrasonic waves

Answer 21

Have the frequencies below the audible range (less the 20kHz)

Question 22

Ultrasonic waves

Answer 22

Have frequencies above the audible range (larger than 20kHz)

Question 23

What type of wave is the speed of sound greater in solids

Answer 23

-Longitudinal waves
-The speed of sound in highly elastic solids, such as steel, reaches 5000-6000m.s^-1

Question 24

What is impedance

Answer 24

Media are characterised by a certain acoustic resistance

Question 25

How can the reflection and transmission coefficients of the sound wave be calculated

Answer 25

By knowing the acoustic impedances of two materials

Question 26

What does a greater difference between the acoustic impedances lead to

Answer 26

The greater part of the incident sound wave is reflected back into the medium

Question 27

What is the Doppler Effect

Answer 27

The apparent change in frequency (or wavelength) that occurs because of the motion of the source or observer of a wave

Question 28

Features of the Doppler Effect

Answer 28

-When the relative speed of the source and the observer is higher than the speed of the wave, the frequency appears to increase -When the relative speed of the source and observer is lower than the speed of the wave, the frequency appears to decrease

Question 29

Sound pressure (p)

Answer 29

The additional periodically changing component of the pressure in the medium is caused by sound propagation. Sound pressure is measured in Pascals (Pa)

Question 30

Wave intensity

Answer 30

For waves, the intensity value represents the energy carried by the wave per unit of time through a perpendicular unit area

Question 31

What is the threshold of hearing

Answer 31

This is the sound pressure level (SPL) of 20 micro pascals

Question 32

What is the absolute threshold of hearing (ATH)

Answer 32

-The minimum amplitude of a pure tone that the average ear with normal hearing can hear in a noiseless environment -The ATH curve rises with age, as the human ear becomes more insensitive to sound

Question 33

What is the threshold of pain

Answer 33

-The SPL beyond which sound becomes unbearable for a human listener -Prolonged exposure to sound pressure levels over the threshold of pain can cause physical damage, potentially leading to hearing impairment

Question 34

What is a pure (simple) tone

Answer 34

A sound with a certain frequency, e.g a tuning fork

Question 35

What is a complex tone

Answer 35

It is made up of multiple simple tones

Question 36

What is the acoustic spectrum

Answer 36

The totality of the fundamental tone and overtones represented by their relative amplitude (relative to the amplitude of the fundamental tone)