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KS4 Physics Using Sound © Boardworks Ltd 2004 Learning Objectives • Understand how sound is heard and the audible frequencies of human hearing • Understand how the loudness of sound is quantified, and what is meant by “noise” • Understand the nature and uses of ultrasound. • Textbook references: 6.06 (p. 134-135) • 6.10 (p. 142-143) Different speeds of sound Breaking the sound barrier! Which of these travel faster than the speed of sound in air? distance (m) time (s) small aeroplane 600 5 jet fighter 900 2 cheetah 50 2.5 meteorite 10 000 0.35 speed (m/s) The jet fighter and the meteorite break the sound barrier. What does this mean? Reflected sound waves What happens when a sound wave meets a hard flat surface? The sound wave is reflected back from the surface. What type of sound does this produce? Echoes and reflection What do we call reflected sound? Are hard or soft surfaces best at reflecting sound? How are echoes reduced in cinemas and theatres? Name two animals that use echoes for navigation or communication. How does the ear hear? 1.Sound waves are collected by the ear lobe or pinna. 6.The auditory nerve takes the signals to the brain. 6 4 1 2 2.The waves travel along the ear canal. 3 5 5.The cochlea turns these into electrical 4.The small bones 3.The waves signals. (ossicles) amplify make the ear the vibrations. drum vibrate. How does the ear hear? Can we hear all frequencies? Set the volume and increase the frequency of the signal provided by the signal generator. Humans cannot hear sounds of every frequency. The range of frequencies you can hear is called your hearing range. What is the hearing range of a healthy young person? Do we have the same hearing? Does everyone have the same hearing range? We all have slightly different hearing ranges but almost 1 in 5 people suffer some sort of hearing loss. Temporary hearing loss may be caused by ear infections and colds after which hearing recovers. Permanent hearing loss and deafness can be present at birth or occur if the ear is damaged or diseased. People lose the ability to hear sounds of high frequency as they get older. Which end of their hearing range will be affected? Comparing hearing ranges Do all animals have the same hearing range? 100 000 10 000 1 000 frequency 100 (Hz) 10 1 0 human dog bat elephant mouse dolphin How is loudness measured? The loudness of a sound is measured in decibels (dB). 0 dB = quietest audible sound (near total silence) 10 dB = 10 times more powerful than the quietest sound 20 dB = 100 times more powerful than the quietest sound How much more powerful than the quietest sound is 30 dB? A whisper is 30 dB and normal conversation is 60 dB. How much more powerful is normal conversation compared to a whisper? When is sound dangerous? Any sound above 85 dB can damage hearing. You know you are listening to 85 dB sound if you have to raise your voice to be heard. What might also influence hearing loss? The amount of time spent listening to a loud sound also causes hearing problems. Any 140 dB sound causes pain and immediate damage! More than two hours of 100 dB sound can damage your ears. Why are there laws about the maximum levels of sound that people should be exposed to at work? What is noise? A noise is any unwanted sound. What one person considers noise another person might not. Can you name any examples? List three effects of noise. List three ways of reducing the effects of loud noise. How loud is loud? decibels aircraft overhead 160 personal stereo 140 permanent ear damage 120 100 loud bell 80 quiet countryside 60 40 pin being dropped circular saw at 2m 20 0 can just be heard What is ultrasound? The upper frequency limit of human hearing 20 000 Hz. Any high frequency sound above 20 kHz is called… ultrasound Whales and dolphins communicate using ultrasound. Why does a dog whistle vibrate at ultrasound frequencies? Can you name another human use of ultrasound? Using ultrasound Which of the following does not use ultrasound? imaging fetuses dolphins jewellery cleaning ultrasonic toothbrush viewing kidney stones bats ultrasonic cleaning echo location submarines It’s a trick question! All of the above involve ultrasound. High frequencies can be very useful! Using ultrasound in medicine Ultrasound is the name given to a medical technique. It uses high frequency sound waves to produce images of inside the body without opening up the body. fetus at 10 weeks fetus at 20 weeks ultrasound for scanning fetuses instead of X XWhy raysisare more energetic and penetrating and are a rays lot more which would give a clearer dangerous, they could causepicture? damage to the growing baby. How does ultrasound imaging work? Ultrasound, like all sound, is reflected when it meets different boundaries. So how is this used for imaging? An ultrasound machine transmits high-frequency sound waves into the body. These sound waves are reflected different amounts by different tissues. The reflected waves are detected by a receiver. A computer turns the distance and intensities of these echoes into a two-dimensional image. Sound multiple choice Learning Objectives • Understand how sound is heard and the audible frequencies of human hearing • Understand how the loudness of sound is quantified, and what is meant by “noise” • Understand the nature and uses of ultrasound. • Textbook references: 6.06 (p. 134-135) • 6.10 (p. 142-143)