Chaper 13: Sound Waves Flashcards
What type of wave is a sound wave?
Longitudinal wave
What are sound waves caused by?
By vibrating objects
What are sound waves made up of?
Compressions and refractions
Where does sound waves move faster in? Can it travel through a vacuum?
In denser materials or mediums. This means that it can’t travel through a vacuum because there aren’t any particles.
How are sound waves displayed?
Oscilloscope displays sound waves and measure their properties. It converts the sound waves into electrical signals.
What is an oscilloscope?
A device which can display the microphone signal on a screen.
If the amplitude is high, what happens to the loudness?
The greater the amplitude the more energy it carries which means it will e louder.
If the frequency is high what happens to the pitch?
If the source has a high frequency, the sound is high pitched. If it has a Lower frequency, the sound is low pitched.
What can humans generally hear sounds in a range of frequencies?
20Hz - 20,000Hz.
What’s 1KHz in Hz?
1000Hz
What are frequencies lower than 20Hz known as?
Infrasound.
What is frequencies above 20,000Hz known as?
Ultrasound
How can we calculate the frequency of a wave using a oscilloscope?
SEE PART 4 SEEINING OR REPRESENTING SOUND
What is the equation to work out the speed of sound?
Distance/Time
Measuring the speed of sound directly between two points - experiment method
Two people stand a distance of around 100m apart.
The distance between them is measured using a trundle wheel.
One of the people has two wooden blocks, which he bangs together above his head.
The second person has a stopwatch which he starts when he sees the first person banging the blocks together and stops when he hears the sound.
This is then repeated several times and an average value is taken for the time.
The speed of sound can then be calculated using the equation.
Measuring the speed of sound using echoes - experiment method
A person stands about 50m away from a wall (or cliff). This distance is measured using a trundle wheel.
The person claps two wooden blocks together and listens for the echo.
The person then starts to clap the blocks together repeatedly, in rhythm with the echoes.
A second person has a stopwatch and starts timing when he hears one of the claps and stops timing 20 claps later.
The process is then repeated and an average time calculated.
The distance travelled by the sound between each clap and echo will be (2 x 50) m.
The total distance travelled by sound during the 20 claps will be (20 x 2 x 50) m.
The speed of sound can be calculated from this distance and the time using the equation.
What do we use ultrasound for mainly (1)? And why is it safer than using X rays?
Use for medical scans such as pre-natal scans of fœtus and wombs. Safer than using X rays as it will not harm living cells.
What are other uses for ultrasound?
To detect things such as tumors in the body. To shatter things such as kidney stones To help tissue to repair Cleaning such as jewelry To clean teeth by shattering the plaque.
How do you use sonar to calculate the depth of water in the ocean?
- The pulse moves down through the water and bounces off the ocean bottom. The transducer is able to pick up thereflectedsound.
- Computers precisely measure the time it takes for the sound pulse to reach the bottom and return.
- In shallow water the soundwaveswill return very fast and in deeper water it will take more time to receive the echoes.
- The depth of the ocean is calculated by knowing how fast sound travels in the water (approximately 1,500 meters per second). This method of seafloor mapping is calledechosounding.
THIS WAS FOR A SPECIFIC QUESTION IN THE END OF UNIT TEST
What is the Doppler Effect?
The apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.
When does the Doppler Effect happen?
When a moving object produces a wave that then is detected by something else that is stationary.
If the item that has a frequency sound, what happens to the frequency as it gets closer to you?
The closer it comes towards you the higher the frequency and the further away it is from you the lower frequency.
If a moving object emits waves, how are the wavefronts described?
The wavefront gets bunched up in front of the object and spreads out behind the object.
When do we use Doppler Effect?
For measuring the flow of blood in arteries and veins
Echocardiograms
Speed cameras.
Using an oscilloscope to measure the frequency of a sound wave
Use a microphone to convert the sound wave into an electrical signal
Adjust the oscilloscopes to obtain a steady trace on the oscilloscope
Aim to get at least 1 whole wave on the screen
Count the number of divisions on the screen for a single wave cycle
Multiply the number of divisions by the oscilloscope settings for the time base to find the time period
Calculate the frequency using frequency = 1/time period
Doppler Effect questions
For example, two people holding a string with a box with a buzzer
Need to say that this is Doppler effect
Need to talk about frequency, wavelength and pitch
