Lecture 2 Flashcards
What is the definition of oscillations
Movements or processes that, to one degree or another, repeat over time
When are oscillations periodic
if: x(t) = x(t+nT)
How is energy transferred in wave motion
Over a distance
The two main types of waves
Mechanical waves
Electromagnetic waves
Mechanical waves
-Some physical medium is being distributed
-The wave is the propagation of a disturbance through a medium
Electromagnetic waves
-No medium required
-For example; light, radio waves and x-rays
What is a wave/process?
The process of propagation of oscillations in a continuous medium
One fundamental property of all waves
The transfer of energy without the transfer of matter
What is the crest
The location of the maximum displacement of the element from its normal position
What is the amplitude (A)
The distance between the resting position and maximum displacement
What is the wavelength
The distance from one crest to the next crest
What is the period (T)
The time interval required for two identical points of adjacent waves to pass by a point
What is the frequency (v)
The number of crests (or any point on the wave) that pass a given point in a unit time interval
Longitudinal waves
Mechanical waves in which the oscillations of the particles are in the direction of propagation of the wave
Transverse waves
Waves in which the oscillations are in a direction perpendicular to the direction of propagation of the wave
Which types of waves can propagate in liquids and solids
-Both longitudinal and transverse waves can propagate in a solid
-Only longitudinal waves can propagate in liquids
Compression and rarefaction definitions
-An increase in pressure is compression
-Decrease in pressure is rarefaction
What is sound
An elastic wave with a frequency in the range of 16-20,000Hz.
This is the hearing diapason of the human ear
3 types of sound waves
-Audible waves
-Infrasonic waves
-Ultrasonic waves
Audible waves
They are within the sensitivity of the human ear (20Hz-20kHz)
Infrasonic waves
Have the frequencies below the audible range (less the 20kHz)
Ultrasonic waves
Have frequencies above the audible range (larger than 20kHz)
What type of wave is the speed of sound greater in solids
-Longitudinal waves
-The speed of sound in highly elastic solids, such as steel, reaches 5000-6000m.s^-1
What is impedance
Media are characterised by a certain acoustic resistance
How can the reflection and transmission coefficients of the sound wave be calculated
By knowing the acoustic impedances of two materials
What does a greater difference between the acoustic impedances lead to
The greater part of the incident sound wave is reflected back into the medium
What is the Doppler Effect
The apparent change in frequency (or wavelength) that occurs because of the motion of the source or observer of a wave
Features of the Doppler Effect
-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
Sound pressure (p)
The additional periodically changing component of the pressure in the medium is caused by sound propagation.
Sound pressure is measured in Pascals (Pa)
Wave intensity
For waves, the intensity value represents the energy carried by the wave per unit of time through a perpendicular unit area
What is the threshold of hearing
This is the sound pressure level (SPL) of 20 micro pascals
What is the absolute threshold of hearing (ATH)
-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
What is the threshold of pain
-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
What is a pure (simple) tone
A sound with a certain frequency, e.g a tuning fork
What is a complex tone
It is made up of multiple simple tones
What is the acoustic spectrum
The totality of the fundamental tone and overtones represented by their relative amplitude (relative to the amplitude of the fundamental tone)
