Waves Flashcards
What are the two types of mechanical waves
Longitutinal waves
Transverse waves
What is a wave
A wave is a periodic (repeating) disturbance which provides a method for the transfer of energy from one point to another without the physical transfer of matter
Mechanical waves
Require a medium in which to propagate
Because it involves the transfer of vibrational energy between particles
Example: sound waves, water waves
Longitutinal waves
Particles vibrate parallel to the direction of energy flow
Examples: earthquake P waves, sound waves
Transverse waves
Particles vibrate in a direction perpendicular to the direction of energy flow
Examples: water waves, string waves, earthquake S waves
Describe field of Electromagnetic waves
Consists of oscillating electric and magnetic fields that are perpendicular to the direction of wave travel
Properties of electromagnetic waves
Can travel in a vacuum with a speed of 3x10^8 m/s
Does not require a medium
Electromagnetic waves can be considered to be transverse because the electric and magnetic fields move perpendicular to the direction of wave travel
How can astronauts communicate with each other in space
Through the use of radio waves
Because they do not require a medium to travel
and can travel through a vacuum (space)
unlike sound waves
Displacement of medium
The distance the particle has shifted from its normal (rest) position
Distance in a water wave
The position of the particle on the after surface
Compression
Where the particles are closer than normal, the pressure is higher than normal
Rarefaction
When he particles are further apart than normal, the pressure is lower
Vibration
A to and fro motion (back and forth)
Cycle
One complete vibration
Period
Symbol T
Time for one complete vibration
Units in seconds
Frequency
The number of complete waves, vibrations or cycles per second .
Symbol f
Units are in hertz (Hz)
Human ears can hear up to what frequency?
20-20 000Hz
It is called the audible range
Amplitude
Symbol A
The size of the maximum particle displacement of a vibrating particle from its mean or equilibrium position
Relationship between amplitude and energy of a wave
High amplitude = high energy wave
Low amplitude = low energy wave
Amplitude of a wave is related to the energy which it transports
Wavelength
Symbol lamda
Distance between two adjacent points in phase
Units in metres
or
The distance the wave travels while a particle makes one complete vibration (that is in a period )
Velocity
Symbol V or c
Distance covered by a wave per unit time (NOT the particle)
What determines a wave’s speed
It is the nature of the medium (particle spacing, particle size, temperature, density) that determines the wave speed
Phase
Symbol phi
The position and motion of a particle at any instant
Particles having the same displacement from their mean position and moving in the same direction are in phase
Ray
A directed line showing the direction of propagation of a wave
Wavefront
Line along crests of progressive waves
Or
A line in the path of wave motion on which disturbances at every point have the same hose
Relationship of speed of sound in solids, liquids and gases
Particles in solids and liquids are closely packed and the vibrations (compressions and rarefactions ) are transmitted more easily in solids and liquids than in gases
Speed of sound in gases < speed in liquids < speed in solids
What happens when a sound wave passes from one medium to another?
The speed of the wave changes
The wave length also changes
frequency remains CONSTANT
Why does the frequency remain constant as a sound wave travels from one medium to another?
Because at the interface (a point where 2 subjects meet and interact), the particles will still bump into each other the same number of times per second.
Why does the wavelength and hence speed change as a sound wave travels from one medium to another?
Because the particles will be displaced though a different distance in a second medium and the second medium has different properties (eg. Density)
What happens to a wave when the temperature of air increases ?
The speed of sound increases
A higher temperature means that the air particles are moving faster (higher Ek) so the transmission of sound from one particle to the next is faster
Pitch
A position on a musical scale
It is related to frequency
Low pitch
Deep or bass sounds
High pitch
High or treble sounds
Relationship between frequency and pitch
Higher frequency, higher pitch
Loudness
The degree of sensation given to a listener’ sears
It is related to the sounds amplitude (or intensity)
Measured in dB decibels
Relationship between amplitude and loudness
Higher amplitude, higher loudness
Relationship of Increase in decibels to amount of energy
Increase in 3dB implied twice the amount of energy
What does quality do?
Gives each instrument it’s characteristic sound
What does quality depend on ?
The instrument’s shape, structure and material from which it is made
These factors affect the harmonics played and their loudness
How do you differentiate between noise and music?
Music or pleasant sounds are characterised by a wave pattern that regularly repeats, whereas
Noises are characterised by random wave patterns that do not repeat
Reflection
Reflection is the rebounding of a wave as it hits a new medium or material
Describe what would happen is parallel rays of light strike a concave mirror? And how it could change as it curves more
Concave mirrors converters the light rays
They are then reflected through a point called the focal point
The curvier, the closer the focal point
Describe what would happen is parallel rays of light strike a convex mirror? And how it could change as it curves more
Convex mirrors diverge (spread) the light rays
The light rays are reflected outwardly
The curvier the mirror, the further apart the light rays diverge
Law of reflection
The angle of incidence (I) is equal to the angle of reflection (r)
What makes a good reflector of light?
A shiny, smooth surface
Regular reflection
Occurs when parallel beam of incident rays remain parallel after reflection
Such as on smooth surfaces like a mirror
Irregular reflection
Occurs when parallel beam of incident rays reflect in what seems to be unpredictable reflections
Such as on rough surfaces like water ( rough - outer sea )
As a sound wave travels between materials it can be
Reflected, transmitted (diffused) or absorbed
What are the properties of good sound reflectors
Smooth, hard surfaces
What is an echo
The reflection of sound that is heard separately from the original sound
Conditions for an echo to happen
There needs to be an time interval of at least 0.1 seconds between the arrival of the original sound and the reflected sound for an echo to be heard
Echoes can be produced by
Sound reflected from buildings, hills and cliffs
Reverberation
Collection of the multiple reflections of sounds that combine to produce a louder richer sound
Conditions needed for reverberation
The reflected sound waves have to reach your ear in less than 0.1 seconds after the original sound
