Vibrations and Sound Flashcards
What is the frequency of a vibrating object? and its unit of measurement
The number of cycles occurring per second. It’s measured in Hertz (Hz)
What form does sound travel in?
Wave
Explain acoustics
The science of designing theatres or concert halls with the correct balance of reflection and absorption of sound
What is reflection of sound
echo
How do we know sound waves undergo refraction
Sounds are heard clearer over water or on a cold
How do we know sound waves undergo diffraction
Can hear around corners
What is the relationship between the frequency and the vibrating source producing it
The frequency of sound is the same as that of vibrating source producing it.
What is the amplitude
The maximum displacement of any molecule from it’s rest position
What type of wave is sound
It needs a medium to travel through. It is a longitudinal wave- the molecules vibrate parallel to the direction in which the compressions and rarefactions travel.
What is the speed of sound in air
331m/s
What s the relationship medium density and the speed of sound in that medium
The denser the medium the greater the speed
What is an overtone
Frequencies are multiples of certain frequency
ex: f is a given frequency
2f is the first overtone
3f is the second overtone
What is loudness of a sound wave what depend on
It depends on the amplitude and frequency of a wave, The greater the amplitude the greater the loudness
What is pitch and what does it depend on
It depends on the frequency of the wave. The higher frequency the higher the pitch. The lower the frequency the lower the pitch
What is the quality of a note and what does it depend on
It depends on the number of overtones present in the note and the relative strengths of the different overtones present
What are the frequency limits of audibility
Highest and lowest frequencies that can be heard by a normal human ear. Range is 20 Hz- 20,000 Hz
What are frequencies above 20,000 Hz called
ultrasonic
What is the natural frequency
Any object free to vibrate will do so at a certain frequencies the predominate of which is it’s natural frequency of vibration
Explain resonance
If frequency of a periodic force is the same as it’s natural frequency the body will vibrate at a large amplitude. This phenomenon is resonance
Give four examples of resonance
Barton’s pendulum
Wire on a sonometer with a tuning fork
Buildings in an earthquake
Shatter glass, natural frequencies is the same as some high notes
What is the threshold of hearing
The smallest sound intensity detectable by the average human ear at frequency of 1kHz
What is sound intensity
It is the rate at a point which sound energy is passing through unit area at rights angles to the direction in which the sound is travelling at that point
What is the unit of sound energy
Watt per square metre Wm^-2
What is sound intensity level measured in
decibels (dB)
What frequencies is the ear most sensitive between
2000Hz and 4000Hz
When sound intensity in Wm^-2 is doubled what happens to the sound intensity level?
Increases by 3dB
What is a sound level meter used for
It uses a dBA (Decibel adapted) scale, to take account of the vibration in the human ears response to sounds of different frequencies
What damage can noise do and why noise protection needed
Partial deafness due to being exposed to loud sounds is incurable.Industry workers/farmers war ear protection when working with loud machinery
Explain a string vibrating at it’s fundamental frequency
A string vibrating with an antinode at it’s centre and a node at either end (with no others) is vibrating at it’s fundamental frequency
What is the relationship between the length of string and its fundamental frequency
Greater the length the lower the fundamental frequency. Fundamental frequency of a string is inversely proportional to it’s length.
f is proportional to 1/l
How can F is proportional to 1/l be verified
With a sonometer - to investigate the variation of the fundamental frequency of a stretched string
Explain harmonics
Frequencies which are multiples of a certain frequency F are harmonics. F is 1st harmonic and the fundamental frequency. 2f is the second harmonic etc…
What is the formula for the fundamental frequency of a string
f= 1/2l (square root of T/mass per unit length)
How is fundamental frequency proportional to Tension
f is proportional to the square root of T
How is fundamental frequency proportional to mass per unit length
f is proportional to 1/square root of mass per unit length
Explain how stationary waves act in a pipe closed at one end
There is a node at the base of the pipe.- molecules do not vibrate
The amplitude increases as you move up and there is an antinode at the top of the pipe- molecules vibrating with a max amplitude.
How does resonance occur in a pipe
If pipe’s length is varied resonance will occur at certain lengths
Explain how stationary waves act in a pipe open at both ends with an example
There must be an antinode at each end.
In open pipe all harmonics may be present.
Tin whistle is an example of a musical instrument which a column of air resonates in a pipe open at both ends
In the experiment variation of the fundamental frequency of a stretched string with it’s tension how is the fundamental frequency determined
Changing tuning fork and adjusting tension until resonance is observed
How would the measurements taken In the experiment variation of the fundamental frequency of a stretched string with it’s tension be shown on a graph
graph of f against graph of square root T as they are proportional
How does the graph of frequency proportional to tension verify that relationship In the experiment variation of the fundamental frequency of a stretched string with it’s tension
there is a straight line through the origin
How would the measurements taken In the experiment variation of the fundamental frequency of a stretched string with it’s length be shown on a graph
plot f compared to 1/l
What is the relationship between fundamental frequency and length as shown in the experiment variation of the fundamental frequency of a stretched string with it’s tension be shown on a graph
f is proportional to 1/l
In the experiment variation of the fundamental frequency of a stretched string with it’s tension how was tension measured
Newton balance
In the experiment to measure the speed of sound in air how was the column of air adjusted, how was the frequency measured and how was the diameter measured
-Open pipe was raised for length
Read the frequency from the tuning fork
Diameter was measured using a vernier calipers
In the experiment to measure the speed of sound in air how was it known the air column was vibrating at it’s first harmonic
The first time resonance - a loud sound is observed
In the experiment to measure the speed of sound in air why do you need to measure diameter of the top of the tube
the wave partially exists above top of tube
How would you find the speed in air doing the experiment to measure the speed of sound in air but not measuring the diameter
You would find the distance between two points of resonance and double this to find the wavelength. multiply wavelength by frequency to get speed
