Sound Waves Flashcards
What type of waves are sound waves?
- Longitudinal waves caused by vibrating objects
- The vibrations are passed through the surrounding medium as a series of compressions.
How can sound waves travel?
- Sound waves can travel through solids (can hear Isabelle and Talia watching H20), liquids (whales can communicate), gases (speaking in the air)
- Travels faster in solids than liquids and faster in liquids than gases (because particles are closer together and so they are able to transfer sound energy more quickly.
Can sound waves travel through a vacuum?
No they cannot because there are no particles to carry the vibrations
What can sound waves do?
- Sound waves can be reflected by hard, flat surfaces but things like carpets, curtains act as absorbing surfaces and so will absorb sounds rather than reflect them
- Sounds waves can refract, as they enter different media (speed up as they enter denser material)
- Sound waves can be diffracted through gaps and around obstacles. This is why you can hear someone talk from around a corner or outside a room, the sound waves will bend and spread out
What is the frequency range for human hearing?
- 20Hz up to about 20,000Hz (20kHz), this spread of frequencies is called audible range or hearing range
- The upper limit is dropped with age and if hearing is damaged with exposure to very loud sounds
How do you measure the speed of sound in air using an oscilloscope?
- Connect a signal generator to a speaker and so you can set the signal generator to give a sound with a frequency of about 1kH.
- The detected waves at each microphone can be seen as a separate wave on the oscilloscope.
- Start with the microphones close together and near to the speaker, then slowly move one away until the two waves are aligned on the display but exactly one wavelength apart
- Measure the distance between the microphones to find the wavelength.
- Then sue the formula v= f x l to find the speed of the sound waves passing through the air, the frequency is whatever you set the signal generator to in the first place.
- The speed of sound in air is roughly 330m/s - 340m/s
What is a reflected sound wave?
An echo
Describe echo sounding
Sound waves are emitted from the ship and travel to the seabed
Equipment on the ship is able to detect some of the sound waves that are reflected by the seabed
The depth of the seabed can be calculated from the time between sending the sound wave and detecting the echo
The system of using echoes in this way is called sonar (Sound Navigation And Ranging)
What are ultrasounds?
sound waves with frequencies above the range of human hearing
What is a medical use of ultrasound?
-Can be used in medicine to produce images of the inside of the human body
A transducer emitting pulses of ultrasound is put into contact with the skin (via a special gel to ensure that the waves get into the body). Each pulse is partially reflected as it meets the boundary between one type of tissue and another and the reflected waves are detected by the same device that emitted them. From the measured travel times a one dimensional map can be constructed of where the boundaries are below the surface of the skin.
The pulses are sent out at different angles so that the ‘line maps’ can be combined to give a fan shaped picture that represents a slice through the body. The frequencies used are about 1MHz.
What are other uses of ultrasound?
- Ultrasonic tape measures to survey rooms
- At sea to locate underwater objects
- Bats to navigate their way round and find prey etc.
- Ultrasound scanning babies, because ultrasound is not a form of ionising radiation so ca be safely used to ‘take’ a lot of pictures which can be combined to make a short movie sequences.
