Sound Waves (T3) Flashcards
How is sound made and why does it get quieter the further away the listener is from it?
- a noise causes air to wobble with vibrations which ripple from the sound source to the detector
- these vibrations spread out constantly and grow weaker as they do so, causing the sound to get quieter the further away the listener is
Why is there no sound in a vacuum?
Sound needs a ‘medium’ (usually air) to vibrate within. Without this, there can be no vibrations and therefore now sound.
What frequency range can the human ear generally hear sounds within and what is this spread of frequencies known as?
- around 20Hz to 20,000Hz
- it’s known as the audible range, or hearing range
Do loud sounds have larger or smaller amplitudes than quiet ones?
Larger
Explain a crude way of measuring the speed of sound…
- find a large flat wall that allows you to hear an echo
- clap your hands at regular intervals so that the echo is heard halfway between each clap
- once a good rhythm has been established, time 20 claps
- measure the distance to the wall and calculate how far the sound has travelled by doubling that figure and multiplying by 20
- speed of sound = distance in metres / time in seconds
Explain how a speaker generates sounds…
- as the speaker cone moves out, it pushes air molecules closer together creating a compression
- these particles then push against neighbouring particles so that the compression appears to be moving in the outward direction of the cone
- behind the compression is a region where the particles spread out, called a rarefaction
- after the cone has vibrated several times it has created a series of compressions and rarefactions travelling away from it
- this is a longitudinal sound wave
What happens when sound waves enter the ear?
They strike the eardrum and make it vibrate. These vibrations are changed into electrical signals which are then detected by the brain.
What mediums can sound waves tested through?
- solids, like when you can hear someone talking from another room
- liquids, like how whales communicate under water
- gases, like the sounds we communicate to each other, vibrating through air
Briefly outline an experiment to show how sounds does not exist in a vacuum, and explain the conclusion of this experiment..
- secure a bell in a jar with a vacuum pump attached to the bottom
- at first you can see and hear the bell ringing, however if you remove the air using the vacuum pump you can still see the bell ring but it cannot be heard
- this shows that light waves can travel through a vacuum but sound waves cannot
What is the approximate speed of sound in the air?
340m/s
What is the speed of sound in seawater?
1500 m/s
What is the speed of sound in a solid such as steel or concrete?
Around 5000 m/s
What is the formula for the speed of sound?
Speed of sound = frequency x wavelength
V = f x λ
How do you measure the speed of sound using an oscilloscope?
- gather two microphones, an oscilloscope, a signal generator and a loud speaker
- connect the microphones to the oscilloscope and the signal generator to the speaker
- set the signal generator to give a sound with a frequency of about 1 kHz
- start with the microphones 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 (you know you have got to this point when the traces on the oscilloscope screen are exactly above one another)
- measure the distance between the microphones to get the wavelength of the sound and use the oscilloscope screen to find an accurate value for the frequency
- the speed of sound can be calculate with the formula v = f x λ
What types of sounds have a high pitch?
- when sound waves vibrate quickly they have a high frequency and are heard as sounds of a high pitch
- for example small objects like the strings of a violin vibrate quickly, producing waves with a high frequency
