03 Waves, Sound and EM Spectrum Flashcards
An ambulance is producing sound represented by wave 2
Which wave would represent the sound an observer would hear as the ambulance approached them?
Wave 3.
The frequency of the sound would increase and wavelength decrease as the ambulance approached the observer.
What is the use of UV radiation?
produced by tanning bed lights to tan skin
used to detect conterfeit money
Give three properties (features) common to all EM waves
They all…
travel at the speed of light
all transverse waves
all transfer energy and information without transferring matter
all travel through a vacuum
Which wave has the largest wavelength?
wave 1
largest distance between adjacent crests
How can you make a transverse wave with a slinky?
Move your hand in a side to side movement
List the EM spectrum in order of decreasing frequency
Gamma
X-ray
UV
Visible
IR
Microwave
Radio
What is blueshift in terms of movement of stars or galaxies?
If a star is moving towards the observer, the wavelength of the light it is producing is squashed.
The observer sees light of a smaller wavelength and higher frequency- it is a different colour as it is shifted towards the blue end of the spectrum
What is redshift in terms of movement of stars or galaxies?
If a star is moving away from the observer, the wavelength of the light it is producing is stretched.
The observer sees light of a larger wavelength and lower frequency- it is a different colour as it is shifted towards the red end of the spectrum
How is wavespeed, wavelength and frequency related?
wavespeed = wavelength x frequency
Label the compressions, rarefactions and wavelength on the longitudinal wave below
What is 204 nm in m?
204 x 10-9 m
What is the Doppler effect?
The apparent** change in frequency (wavelength) of sound (or light) due to **relative movement between an object an observer.
How can you make a longitudinal wave with a slinky?
move your hand in a forwards and backwards movement
Sketch a graph of how frequency varies with time as an object approaches an observer, passes them and then travels away from them.
Higher than normal frequency as car approaches
Lower than normal frequency as car move away
Black horizontal line is the actual frequency of the sound
How would you measure the frequency of waves passing a jetty?
Time how long it take for 10 waves to pass the end of the jetty
frequency = 10 waves / time for 10 waves to pass
An ambulance is producing sound represented by wave 2
Which wave would represent the sound an observer would hear as the ambulance travelled away from them?
Wave 1.
The frequency of the sound would decrease and wavelength increase as the ambulance moves away from the observer.
Fred noticed that 10 waves passed a point in 5 seconds. What is the frequency of the wave?
frequency = 10 waves/ 5 s
= 2 Hz
What is 700 micrometres in metres?
700 x 10-6 m
Fred noticed that 10 waves passed a point in 5 seconds. What is the period of the wave?
Time period = 5 seconds / 10 waves
= 0.5 seconds for one wave to pass
Which wave has the largest amplitude?
wave 2
It has the largest displacement from the equilibrium
What is the unit for time period?
seconds or s
What is the unit for amplitude?
metres (m) or decibels(dB)
What has a larger wavelength?
Infrared or gamma?
Infrared
Match the following terms with their definition
frequency- the number of waves going past in one second
wavelength- the length of one repeat of the wave pattern
wave speed- how far a wave travels in one second
Why are UV waves dangerous?
They can damage the retina and damage eye sight
They can cause skin cancer
What is the use of microwaves?
produced by microwaves to cook food
produced by mobile phones to communicate
Produced by satellites to send signals to satellite dishes
What is a transverse wave?
Where the oscillation is 90° to the direction of wave travel
How do the waves of red light differ from waves of violet light
ROY G BIV
Red light-larger wavelength and lower frequency- it has less energy
Blue light- smaller wavlength and higher frequency- it has more energy
What are the uses of infrared radiation (IR)
emitted by ovens to cook food
emitted by radiators to heat houses
emitted by tv controllers to control t.v.
What is the relationship between wavelength and frequency of a wave?
As wavelength increases, frequency decreases
They are inversely proportional
What is the use of X-rays?
Used to detect breaks in bones
used to detect crystal structure in salts
List the EM spectrum in order of increasing frequency
Radio
Microwave
IR
Visible
UV
X-ray
Gamma
What is the relationship between time period and frequency?
time period = 1 / frequency
or
frequency = 1 / time period
Label the wavelength, amplitude, crest and trough of the transverse wave below
If a star is moving very quickly away from an observer it is possible that the light can no longer be observed with the naked eye. Explain.
The light’s wavelength is shifted so far to the red end of the spectrum that its wavelength is the same as infrared light and is invisible to the naked eye.
Which wave has the highest frequency?
wave 3
it has more waves per second
Galaxies rotate
If one side of the galaxy is moving toward us and one side is moving away from us, what would we observe in terms of the light we receive from each side of the galaxy?
Side moving towards us will be blueshifted, the light will have a smaller wavelength and higher frequency- shifted towards the blue end of the spectrum
Side moving away from us will be redshifted, the light will have a large wavelength and lower frequency- shifted towards the red end of the spectrum
How can speed of sound through air be measured in a laboratory?
- connect two microphones to a microsecond timer
- place the two microphones 2.00 metres apart using two metre rules
- place padding under each microphone to prevent sound travelling through the table
- create a sharp sound behind the first microphone
- record the time it takes for the sound to travel from microphone 1 to microphone 2
- repeat five times and calculate the mean time
- calculate the speed of sound through air by
s = 2.00 m / mean time
How can speed of sound through a lab bench be measured in a laboratory?
- connect two microphones to a microsecond timer
- place the two microphones face down on a lab bench 2.00 metres apart using two metre rules
- create a sharp tap to the lab bench behind the first microphone
- record the time it takes for the sound to travel from microphone 1 to microphone 2
- repeat five times and calculate the mean time
- calculate the speed of sound through air by
s = 2.00 m / mean time
How can speed of sound through air be measured in the playground?
- stand exactly 50.00 metres from a large wall of a building
- strike two metal bars repeatedly until a ryhthm is set up and the metal bar is being hit together at the same time the echoes returns.
- start the stopwatch on one strike and time 20 complete strikes.
- This time is how long it take the sound to travel to and from the wall 20 times or 100.00 x 20 = 2000 m
- speed of sound is s = 2000 m / time
Speed of sound can be measured accurately using a stopwatch.
If a starting pistol is used, the people timing must start the stopwatch when they see the smoke from the pistol and then stop it when they hear the sound.
How can you ensure that the speed of sound is measured accurately and what assumption is made?
- very large distances must be used as human reaction time introduces large uncertainties in time measurements
The assumption is that the light reaches the person immediately.
The position of imperfections in a metal can be located using ultrasound.
An ultrasound pulse is sent into the metal and reflections received. If the speed of sound in the metal is 5000 m/s and the echo received 20 microseconds later.
How can the distance to the imperfection be calculated?
20 microseconds = 0.00002 s
divide time by 2
time to imperfection = 0.00002 s / 2 = 0.00001 s
d = s x t
distance = 5000 m/s x 0.00001 s = 0.05 m or 5 cm
Bats locate their prey by echosounding.
They use pulses of ultrasound and listen for the echo with their large ears. If the time between the pulse and echo is small, the insect is closer to the bat.
Name another animal which uses echo sounding.
dolphins
When calculating the distance in an echosounding question, what is the most common error?
The distance calculated from the speed of sound and time for echo must be divided by two!
What is the human hearing range?
20 - 20 000 Hz
What is ultrasound?
Any sound over 20 000 Hz
Ultrasound is used to image babies in the womb.
An image is formed on the screen if reflections are received from the different surfaces (layers) of the baby.
How does the time for the reflection relate to the distance to the surface?
The further the surface is from the ultrasound transmitter/receiver, the longer it takes for the echo to return.
The distance to a storm can be calculated using the lightning seen and the thunder heard.
What assumption is made in this calculation?
As the pitch of sound increases, what happens to the distance between the compressions?
distance between compressions decreases
