1. SPH3U UNIVERSITY PHYSICS
WAVES & SOUND
 Nature & Sound Waves
(P )

2. Reflection of Sound Waves
Just as a mirror reflects light, when sound waves radiating out from a source strike a rigid obstacle, the angle of reflection of the sound waves equals the angle of incidence. Thus sound waves conform to the Laws of Reflection.
REFLECTION OF SOUND
sound waves obey the laws of reflection
September 21, 2018
3U5 - Nature & Sound Waves

3. Reflection of Sound Waves – DYK?
Sound waves emitted at the focal point of a curved reflector are reflected in a specific direction. If the sound waves encounter a curved surface, they are reflected to a specific area, and thus, are concentrated. For example, in the dome of St. Paul’s Cathedral, whispers can be heard clearly 32 m away.
September 21, 2018
3U5 - Nature & Sound Waves

4. Applications of Reflection
Echoes are produced when sound is reflected by a hard surface, such as a wall or cliff. The echo-sounder is a device that uses sound reflection to measure the depth of the sea.
ECHO
produced when sound is reflected by a hard surface
September 21, 2018
3U5 - Nature & Sound Waves

5. Applications of Reflection
Similar equipment is used in the fishing industry to locate schools of fish. More sophisticated equipment of the same type is used by the armed forces to locate submarines. All such devices are called sonar (sound navigation and ranging) devices.
SONAR
sound navigation and ranging
September 21, 2018
3U5 - Nature & Sound Waves

6. Applications of Reflection
A similar technique, using radio waves to detect the presence of objects in the atmosphere, is called radar (radio detection and ranging). Radar was designed shortly before World War II. Its primary purpose was to detect the presence of aircraft. Today, radar is used for a wide array of applications, but primarily to detect precipitation and other meteorological events (ie Doppler radar).
September 21, 2018
3U5 - Nature & Sound Waves

7. Applications of Reflection
Sound waves can also be used to study Earth’s interior. Most minerals and fuels are deep underground – 1000 m or deeper. Drilling is time-consuming and expensive, so companies will not drill until they are reasonably sure something of value is beneath the ground.
September 21, 2018
3U5 - Nature & Sound Waves

8. Diffraction of Sound Waves
But not only can sound reflect, it can diffract or bend. Have you ever noticed that you can hear the sounds of a classroom through an open door, even though the other students may be out of sight and separated by a wall? You can also easily hear sounds travelling through an open window and even around the corner of a building. This “sound around the corner” effect is so familiar to us that we do not give it a second thought.
September 21, 2018
3U5 - Nature & Sound Waves

9. Diffraction of Sound Waves
Sound waves can travel around corners because of diffraction. And how much the sound wave bends depends on both the wavelength and the size of the opening in the barrier.
DIFFRACTION
describes how waves bend, or change direction, as they travel around the edges of obstacles
September 21, 2018
3U5 - Nature & Sound Waves

10. Diffraction of Sound Waves
For the same opening, long-wavelength waves are diffracted more than short-wavelength waves. And decreasing the size of the opening will increase the amount of diffraction.
September 21, 2018
3U5 - Nature & Sound Waves

11. Diffraction of Sound Waves
DIFFRACTION (cont …)
the amount depends on the size of the obstacle or opening in relation to the wavelength of the wave
September 21, 2018
3U5 - Nature & Sound Waves

12. Diffraction of Sound Waves
PRACTICE 1. If a marching band is approaching on a cross street, which instruments will you hear first, a high pitched piccolo or a low pitched bass drum? Explain.
September 21, 2018
3U5 - Nature & Sound Waves

13. Cats & Sound Waves
House cats have excellent hearing, among the best of any mammal (55 Hz to 79 kHz). They also have large movable pinnae (ears), which help amplify the sound and sense the direction form which the sound is coming. This is extremely helpful in hunting.
September 21, 2018
3U5 - Nature & Sound Waves

14. Cats & Sound Waves
NOTE! Cats can see in dim lighting but, in doing so, sacrifice some detail and the perception of some colours. As a result, cat vision is poor up close. They often compensate for this by using their large pinnae to detect the high-pitched noises produced by their prey at the end of the hunt.
September 21, 2018
3U5 - Nature & Sound Waves

15. Echolocation – Dolphins, Orca Whales, & Bats
Dolphins and orca whales rely on the production and reflection of sound to navigate, communicate, and hunt in the dark and murky waters. The location of an object using reflected sound is called echolocation.
ECHOLOCATION
location of an object using reflected sound
September 21, 2018
3U5 - Nature & Sound Waves

16. Echolocation – Dolphins, Orca Whales, & Bats
Both animals produce clicks, whistles, and other sounds that vary in intensity, frequency, and pattern. Scientists speculate that the lower frequency sounds ( kHz) are probably used for communication, while the higher frequencies ( kHz) are probably used for echolocation.
September 21, 2018
3U5 - Nature & Sound Waves

17. Echolocation – Dolphins, Orca Whales, & Bats
In the dolphin, the clicks pass through the melon, which acts as an acoustical lens focussing the sound waves in a beam in front of the dolphin. These sound waves bounce off objects in the water and return to the dolphin as an echo. The fat-filled cavities in the lower jawbones then conduct these vibrations to the ear. The brain then receives this information as nerve impulses, enabling the dolphin to interpret the meaning of the echoes.
September 21, 2018
3U5 - Nature & Sound Waves

18. Echolocation – Dolphins, Orca Whales, & Bats
Most bats use echolocation for navigation in the dark and for finding food. The bat can identify an object by the echo and can even tell the size, shape, and texture of a small insect. If the bat detects a prey, it will generally fly toward the source of the echo, continually emitting high frequency pulses until it reaches its target and scoops the insect into its wing membranes and into its mouth.
September 21, 2018
3U5 - Nature & Sound Waves

19. Echolocation – Dolphins, Orca Whales, & Bats
used in sonar applications including:
navigation
mineral and oil exploration
food collection by some animals (dolphins, whales, bats)
September 21, 2018
3U5 - Nature & Sound Waves

20. Nature & Sound Waves
PRACTICE 2. A woman makes a sound and 3.5 s later, the echo returns from a nearby wall. How far is the woman from the wall, assuming that the speed of sound is 350 m/s? d = 610 m
September 21, 2018
3U5 - Nature & Sound Waves

21. Nature & Sound Waves
PRACTICE 3. A ship is travelling in a fog parallel to a dangerous, cliff-lined shore. The boat whistle is sounded and its echo is heard clearly 11.0 s later. If the air temperature is 10C, how far is the ship from the cliff? d = 1900 m
September 21, 2018
3U5 - Nature & Sound Waves

22. Nature & Sound Waves
PRACTICE 4. A ship is anchored where the depth of water is 120 m. An ultrasonic signal sent to the bottom of the lake returns in 0.16 s. What is the speed of sound in water? v = 1500 m/s
September 21, 2018
3U5 - Nature & Sound Waves

23. Nature & Sound Waves
PRACTICE 5. Ultrasonic sound is used to locate a school of fish. The speed of sound in the ocean is 1.48 km/s, and the reflection of the sound reaches the ship 0.12 s after it is sent. How far is the school of fish from the ship? d = km
September 21, 2018
3U5 - Nature & Sound Waves

24. Nature & Sound Waves
PRACTICE 6. Echolocation only works well when the object is as long as or longer than one wavelength of the sound produced. (a) Why do you think bats need to use such high frequencies for echolocation? (b) because their prey is so small
September 21, 2018
3U5 - Nature & Sound Waves

25. Nature & Sound Waves
PRACTICE 7. Echolocation only works well when the object is as long as or longer than one wavelength of the sound produced. (b) Estimate the size of the smallest object a bat can detect using echolocation when the air temperature is 22C. Use a frequency of 110 kHz. (b) min = 3.1 x 10-3 m (3.1 mm)
September 21, 2018
3U5 - Nature & Sound Waves

26.  Check Your Learning
TEXTBOOK P.474 Q.2,6,8 P.397 Q.11 WIKI (SOUND) .... 3U5 - QUIZ2 (Sound - Part 2)  you can complete now!
September 21, 2018
3U5 - Nature & Sound Waves