Sound And Waves Flashcards
Do mechanical waves need a medium
Yes
What is the name for how mechanical waves are made?
Made by a disturbance in the medium
What is a disturbance
A source of energy causing a vibration
How do mechanical waves cause a disturbance in the medium?
They pass along a medium causing the particles of the medium to vibrate, this is passed from one particle to its Neighbour
What is the overall motion of particles in mechanical waves
Zero
3 examples of mechanical waves
Sound waves
Ultrasound waves
Waves on water
Do electromagnetic waves need a medium?
No
Can electromagnetic waves pass through a medium?
Yes, but travel faster in a vacuum
What do electromagnetic waves consist of ?
Varying electric and magnetic fields
3 examples of electromagnetic waves
Light
Radio waves
X-rays
What do progressive waves consist of
Energy moving away from a source
Energy is transferred from one place to another
1 example of progressive wave
From our voices
Is there a difference between progressive waves and standing waves
Yes
In a transverse wave the medium and energy are…
At right angles to each other
Transverse wave
The direction in which the energy travels is perpendicular to the direction of vibration or the particles of the medium
Lambda
Wavelength
Wavelength of a transverse wave
The distance between 2 successive crests
f
Frequency
Unit of wavelength
Meter
Frequency
The Number of complete oscillations (top of one crest to the next ) made by a point in one second
Unit of frequency
Hertz (Hz)
Amplitude
The maximum displacement of a particle of the medium from its mean position
c
Speed of wave
Speed of wave =
Frequency x wavelength
c=
f x lambda
Longitudinal wave
The direction in which the energy travels is parallel to the direction of vibration of the particles of a medium
Regions of high particle density of a longitudinal wave
Compressions
Regions of low particle density of a longitudinal wave
Rarefactions
Wavelength of a longitudinal wave
Distance between 2 successive compressions
Speed of radio wave
Equal to speed of light, not sound
Speed of light
3 x 10 8 m/s
Speed of sound
340 m/s
Source
Origin of wave
Ray
A line which shows the direction of travel of the wave
Wavefront
Concentric circles around the source
Wavelength on a wavefront
Distance between 2 consecutive wavefronts
Diffraction
The spreading if a wavefront into the geometrical shadow when it passes through a gap or around an obstacle
Diffraction is much more noticeable when
The size of the gal or obstacle is approximately equal to or less than the wavelength of the wave
Why do sound waves easily diffract as they pass through an open door
Because the wavelength of a sound wave is approximately equal to the width of an open door
How can you demonstrate the diffraction is light waves
Using a diffraction grating
What is the limit on how thin a fiber can be seen through an optical microscope
No smaller than the wavelength of light
Interference
When waves from coherent sources meet and combine
Constructive interference
Gives a wave of greater amplitude
Destructive interference
Gives a wave of smaller amplitude
Coherent sources
Emit waves of the same frequency and the waves are in phase or have a constant phase difference
In phase
Syncronised
Condition for constructive interference
Waves are in phase and have the same frequency
The crest of one wave meets the crest of another
Condition for destructive interference
When the waves meet they are out of phase with a path difference of lambda over 2 or a multiple of this
The crest of one wave meets the trough of another
Use of destructive interference
Noise reduction
Stationary waves arise from
The combining of 2 progressive waves of the same amplitude, frequency and speed and moving in opposite directions
Energy and standing waves
Large amounts of energy are stored in standing waves, there is no transmission of energy
2 places stationary waves are produces
On the strings of string instruments
In the air columns of wind instruments
Node
Part of standing wave that doesn’t move
Antipode
Part of a standing wave that moves like crazy
The wavelength of a stationary wave
Twice the distance between successive nodes
(Or twice the distance between 2 successive antinodes
How do we knew that sound is a wave?
Interference is a phenomenon associated with waves. Sound exhibits interference, therefore it is a wave
A box that makes noise
Signal generator (SG)
Displays frequencies on a screen
Oscilloscope
Why is CO2 used to show the refraction of sound
It’s the perfect density for the experiment
Doppler effect
The apparent change in the frequency of a wave due to the relative motion between the source and the observer
source moving towards observer 3
Wavefronts closer together
Smaller observed wavelength
Observed frequency is higher
Source moving away from observer 3
Wavefronts further apart
Observed wavelength longer
Observed frequency lower
fo =
fsc
—
c +/- u
Is rise and fall of frequency due to Doppler effect symmetrical
No
How to change angular speed to linear speed
v = rw
Moving towards observer
-
Moving away from observer
+
Star moving towards earth
Looks blue
Star moving way from earth
Looks red
2 medical uses of Doppler effect (only used when asked for)
Echocardiogram - blood flow measurement
Ultrasound - foetal heartbeat
2 uses of Doppler effect
Checking the speed of a car
Studying the stars
2nd harmonic =
1st overtone
5th harmonic =
4th overtone
Pitch
Related to the frequency of a sound
Higher frequency = higher pitch
Quality of a sound
Depend of the number and intensity of harmonics present
Loudness of a sound
Depends on the amplitude of the vibrations of a sound wave
Subjective
3 characteristics of a sound
Pitch
Quality
Loudness
When a system that is capable of vibrating is made it vibrate
It will do so at its natural frequency
Forced frequency
External vibration force acts on a system that is capable of vibrating at that frequency
What is resonance
The transfer of energy between 2 bodies of the same natural frequency
When does resonance happen
When the forced frequency is equal to the natural frequency
T=
2pi root (l over g)
f =
1/T
f
Frequency
l
Length of string
T
Tension
u
Mass per unit length
n
Number of harmonic
How do you see resonance on a string
Paper rider falls off
Open close pipe under the fraction line
4
Open open pipe under the fraction line
2
Good quality instrument and why
Open open pipe
Can have all harmonics
d
End correction
How do you get d
I internal diameter x .3
What do you measure diameter with
Sliding callipers
how do you get u from the graph of frequency of a stretched string against 1/length
slope = f/1/l = f x l u = t/4l squared f squared u = T/4(slope) squared
how do you get u from the graph of frequency of a stretched string against root T
slope = f/root T u = (1/4lsquared)(T/f sqaured)= (1/4lsquared)(rootT/f) squared u = (1/4l sqaured) x (1/slope)squared
