1. Sound – Part 3 Year 7 Science

2. Sound Intensity Now, we found the rate at which particles vibrate affects the pitch of the sound and frequency. The magnitude or amplitude at which the particles vibrate affects the loudness of sound. We hear different intensities of sound as different levels of loudness. High intensity sounds are very loud. Similarly low intensity sounds are often quiet.

3. Sound Intensity Sounds are all around us and we live in a noisy world !! Our hearing organs are very delicate and can be easily damaged by high intensity sounds. Sometimes the damage is temporary and at other times it can be permanent - resulting in deafness. For those whose jobs are at airports there is a real risk of becoming deaf. So we need to be able to measure sound intensity so we know when to protect ourselves in dangerously noisy environments. How do we do this???

4. Measuring Sound Scientists measure sound levels with a special unit called a decibel – pronounced “dess-i-bell”. The decibel is written as dB. The softest sound that an average ear can hear is called 0 dB. This is called the threshold of hearing.

5. Decibel (dB) levels of various sounds

6. A safe work environment In the workplace it is important to create a safe and comfortable environment in terms of sound. The law limits both the intensity and amount of time we should be subjected to sound for a safe environment.

7. Hearing and Age When you are young, you hear high-pitched and low-pitched sounds equally well. Throughout life noise damages the more sensitive receptors – those that detect higher pitched sounds. As a result older people usually hear low- pitched sounds better than high-pitched sounds.

8. Loud Noises and Hearing Loss Loud noises (85 decibels or more) for any length of time can cause permanent damage and hearing loss as shown in the graph below:

9. Hearing Aids For thousands of years people with hearing loss used horns to improve their hearing (remember how cats have large ‘auricles’ for better hearing).

10. Modern Hearing aids Electric hearing aids were invented around 1900 with modern units using electronic components.

11. Actual Hearing Aid Units

12. A Cochlear Implant A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf. The implant consists of an external portion that sits behind the ear and a second portion that is surgically placed under the skin.

13. A Cochlear Implant

14. A Cochlear Implant has the following parts: A microphone, which picks up sound from the environment. A speech processor, which selects and arranges sounds picked up by the microphone. A transmitter and receiver/stimulator, which receive signals from the speech processor and convert them into electric impulses. An electrode array, which is a group of electrodes that collects the impulses from the stimulator and sends them to different regions of the auditory nerve.

15. What is Ultrasound Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines.

16. How do Ultrasound machines work In ultrasound, the following events happen: The ultrasound machine transmits high-frequency sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the ones shown in the next slides:

17. Ultrasound Image 1

18. Ultrasound Image 2

19. Dolphins and Echolocation Echolocation – the location of objects by their echos is a highly specialized faculty that enables dolphins to explore their environment and search out their prey in a watery world where sight is often of little use.

20. Dolphins and Echolocation

21. The dolphin is able to generate sound in the form of clicks, within its nasal sacs, situated behind the melon. The frequency of this click is higher than that of the sounds used for communication and differs between species.

22. Dolphins and Echolocation The echolocation system of the dolphin is extremely sensitive and complex. Using only its acoustic senses, a bottlenose dolphin can discriminate between practically identical objects which differ by ten per cent or less in volume or surface area.

23. Breaking the sound barrier When an aeroplane moves faster than the speed of sound, it pushes aside air particles with great force – creating a shock wave. It forms a cone of highly pressurised air particles. A sonic boom is heard when waves at the base of this pressurised cone strike someone's ear. Sonic booms are so loud they can shatter windows and burst ear drums.

24. Sonic Boom due to supersonic jet