Sound Flashcards
sound waves are … waves
sound waves are longitudinal waves
when are longitudinal waves produced?
when the vibrations are parallel to the direction of energy
what three things can sound waves be?
reflected
refracted
diffracted
what are sound waves reflected off?
surfaces
what do we hear sound reflections as?
echoes
what surfaces are good at reflecting sound?
hard, smooth surfaces
what surfaces are good at absorbing sound?
soft, rough surfaces
what is refraction?
a change in direction
what happens when sound waves are refracted?
they change speed when they pass across the boundary between two substances with different densities which causes them to change direction
what is diffraction?
when waves spread out to some extent into the area beyond the gap
what happens when sound waves are diffracted?
when waves meet a gap in a barrier they carry on through the gap
the waves spread out to some extent into the area beyond the gap
in diffraction, what does the extent of the spreading depend on?
the width of the gap compared to the wavelength of the wave
in diffraction, a gap similar to the wavelength causes what?
a lot of spreading
in diffraction, a gap much longer than the wavelength causes what?
little spreading
what is the frequency range for human hearing?
20Hz - 20, 000Hz
what is the speed of sound in air?
343 m/s
describe an experiment to measure the speed of sound in air
connect two microphones to a computer which will measure the sound
place the two microphones at a calculated distance apart (e.g. 3 metres)
make sure you are in a silent area and then ring a bell near one of the mircophones
use the equation speed = distance ÷ time to calculate the speed of sound in air
what does the pitch of sound depend on?
the frequency of the vibration of the source
the greater the frequency, the … the pitch
the greater the frequency, the higher the pitch
the lower the frequency, the … the pitch
the lower the frequency, the lower the pitch
what does the loundness of a sound depend on?
the amplitude of vibration
the greater the amplitude, the … the sound
the greater the amplitude, the louder the sound
the smaller the amplitude, the … the sound
the smaller the amplitude, the quieter the sound
what is the wave equation?
wave speed (m/s) = frequency (Hz) x wavelength (m)
v = f x λ
sound requires a … to transfer …
sound requires a medium to transfer energy
what can the medium that sound requires be?
a soild, liquid or gas
what vibrates when sound travels?
the medium vibrated as the waves travel though
sound travels faster in … mediums
why?
sound travels faster in more dense mediums
an increase in particle density increases the speed of sounnd as particles are slow to react to change in motion
why does sound travel slower in more dense mediums?
increase in particle density will decrease the speed the speed of soud
the particles are slow to react to changes in motion
which axis is time always on? why?
the x axis
it is independent as you can never change it
the graphs show oscilloscope traces produced by four different sounds
which graph shows the trace for the loudest sound and lowest frequency?
PICTURE
B
the distance = 1.45 m
the time = 4.6 ms
calculate the speed
speed = distance ÷ time
convert ms into s - 4.6 ÷ 1000
1.45 ÷ 0.0046
= 315.22 (2 d.p) m/s
in an experiment to measure the speed of sound, how can you make the experiment a valid test?
keep the temperature of the room the same
in an experiment to measure the speed of sound, suggest two ways in which the student could improve the quality of their data
repeat each distance at least three times and calculate an average
perform the experiment in a background sound cancelling booth to eliminate any interferance fom background sound or reflections from the wall
what is an analogue signal?
a signal that can be formed from a range of frequencies and amplitude
they are converted into electrical voltages or currents that vary continuosly in amplitude and frequency
what is a digital signal?
signals that are made of two discreet values (on and off)
then the signals have thier backgroundnois removed before being amplified
give one advantage of using digital signals
digital signals carry more information per second than analogue
a CD player is connected to a loudspeaker system
the sound producd has a range of frequencies
use ideas about diffraction to explain why different frequencies require different sizes of loudspeaker
large wavelengths need large speakers for optimum diffraction
small wavelengths need small speakers for the same optimum diffraction
frequency and wavelength are inversely proportional
the frequency of sound wave P is 250 Hz
find the time period
T = 1 ÷ f
= 1 ÷ 250
=0.004 s
find the frequency of Q when Q has double the time period of P and P has a frequency of 0.004
F = 1 ÷ T
= 1 ÷ 0.004
= 250 x 2 (double the time period)
= 500
what is the equation for frequency?
F = 1 ÷ T
what is the eqaution for time period?
T = 1 ÷ f
describe how sound waves move through the air
sound is created by vibrating objects
the vibrations of the object set particles in the surrounding medium in vibrational motion thus transporting energy through the medium
for a sound wave travelling through the air, the vibrations of two particles are describes as longitudinal waves (when the motion of the particles are parallel to the energy transfer)
Andrews readings: 0.44, 0.46, 0.44, 0.48, 0.43
state the precision of Andrew’s readings
state means give a value
0.01s (the smallest incrament in his readings)
Andrews readings: 0.44, 0.46, 0.44, 0.48, 0.43
Calculat the speed of sound in m/s if the distance is 150m
use an appropriate figure of significant figures
why did you choose this number of significant figures?
mean (average) time in s = 0.45
speed = distance ÷ time
= 150 ÷ 0.45
= 330 (2sf)
look at the number of significant figures that they (Andrew) used - 2
you follow suit
the oscilloscope settings are:
Y direction: 1 square = 1V
X direction:1 square = 0.001s
how many time periods are shown in the trace?
three
(see trough to trough as one)
the oscilloscope settings are:
Y direction: 1 square = 1V
X direction:1 square = 0.001s
calculate the frequency of one time eriod
f = 1 ÷ T
T = time for 1 period
T = 2 x 0.001 (two squares = 1 time period)
T = 0.002
f = 1 ÷ T
= 1 ÷ 0.002
= 500Hz
describe an experiment to measure the speed of sound in air using an oscilloscope
attach two microphones to the oscilloscope
you will also need a signal generator which will need to be attached to a loudspeaker
set the signal generator to give a sound with a specific frequency
start with the microphone close together and observe how the two traces on the oscilloscope compare
then move one microphone further away from the loudspeaker until it is one complete wavelength away from the first
measure the distance between microphones to get a wavelenth of the sound
the frequency is the specific frequency you set it to earlier
use the speed of sound equation: speed = distance ÷ time
some aeroplanes can travel faster than the speed of sound
when an aeroplane travels faster than the speed of sound it casues a shock wave
people on the ground hear this shock wave as a sonic boom
a student says: “It is easier for an aeroplane to make a sonic boom when it travels higher up.”
do you agree with the student?
yes, i agree
as shown by the graph, the higher above sea level something is, the slower the speed of sound
thus, as an aeroplane travels higher, the speed of sound gets slower so it is easier for an aeroplane to travel faster than sound so it is easier for an aeroplane to make a sonic boom
give an example of a transverse wave
a light wave
describe how longitudinal waves and transverse waves differ
longitudinal waves are parallel to the direction of energy whilst transverse waves are perpendicular to the direction of energy
How do you measure frequency on an oscilliscope?
The horizontal axis on the display is the time. The time between each division on the scale can be adjusted to get a clear, readable trace
- Adjust the time division setting unti the diplay shows at least one complete cycle
- Read off the period - the time taken for one complete cycle
e. g. here 1 cycle crosses 20 divisions, where each division is 0.00001 s (from the setting) so period = 20 x 0.00001 s = 0.0002 s - Frequency = 1 ÷ 0.0002 s = 5000Hz = 5kHz
This is the original sound. What would the trace look like if the pitch was higher?
This is the original sound. What would the trace look like if the pitch was lower?
This is the original sound. What would the trace look like if the pitch was lhigher and the sound louder?
Can sound travel in a vaccum? Why?
sound cannot travel in a vaccum because there are no particles in a vaccum and sound waves are ccaused by vibrating particles
Information in converted into … which can be either … or …
Information in converted into signals which can be either analogue or digital
Both digital and analogue signals … as they travel, so they need to be … along their route
They also pick up … or … from electrical disturbances or other signals
Both digital and analogue signals weaken as they travel, so they need to be amplified along their route
They also pick up interference or noise from electrical disturbances or other signals
What advantage do digital signals have over analogue signals?
When you amplify an analogue signal, the noise is amplified too - so every time it’s amplified, the signal loses quality
With a digital signal, the noise is just ignored, so the signal remains high quality
What is interference? What is an example of this?
when two or more waves of a similar frequency meet, they can create one combined signal with a new amplitude - this is a called interference
e.g. when two radio stations transmit on similar frequencies
What is multiplexing?
transmitting multiple signals at the same time with just one cable or EM wave
Which type of signal is it easier to do the process of multiplexing? Why?
digital signals
if analogue waves are of similar frequency, it casuses interference when the signal loses quality
with digital signals it is much easier to tell them apart, so you can transmit more information along the same channel
What is quantisation?
the process of ‘rounding’ multiple valuesto a smaller set
by doing this, you can pack more information into the same amount of space
Which type of signal is better at quantisation? Why?
digital signals can only have two values (on and off) so quantisation doesn’t lose much information
with analogue, a lot of information is lost when a continuos range is rounded off
