Reflection Of Sound Part 2

1. 1
REFLECTION OF SOUNDREFLECTION OF SOUND
•The reflection of sound follows the same laws
as for reflection of light
–angle of incidence = angle of reflection
–the incident wave, the reflected wave and the
normal lay in the same plane.
•Sound waves can be reflected by large, hard,
smooth, vertical and faraway surfaces, e.g.
walls, buildings and cliffs.
•Echoes are produced by the reflections of
sounds from such surfaces.

2. 2
REVERBERATIONREVERBERATION
•This occurs when the original and reflected
sounds are so close that the two cannot be
heard as separate sounds. The original sound
just seems prolonged.

3. 3
Applications of Sound
Echo is a reflection of sound.
Echoes are used to
find objects under
water. This is called
echolocation .

4. 4
Applications of Echo
1To find submarines from surface
ships.
2In fishing boats, to find large shoals
of fish.
3To measure the depth of the sea.
4to locate a sunken shipwreck or
cargo

5. 5
1To find
submari
nes
from
surface
ships.

6. 6
2In fishing
boats, to
find large
shoals of
fish.
3To
measure
the depth
of the sea.
Refer to TB pg. 216

7. 7
Nature of sound waves:
1 are longitudinal waves
2 need a medium to travel
3 can be reflected
4 travel faster in a denser medium than in
the less dense medium.
5 travel at a speed of 330 m/s in air at 25°C

8. 8
Pitch and Frequency
The sounds produced by the mouse and
the girl are high pitch sound.

9. 9
Pitch
In musical scales, doubling the frequency
of a note produces a sound one octave
higher than the original sound. Halving the
frequency produces a sound one octave
lower.
In general, higher frequency sound gives
rise to higher pitch note.
Refer to TB pg. 220

10. 10
Compare the frequencies of sound with same
loudness:
Lower pitch sound with lower frequency
Higher pitch sound with higher frequency

11. 11
Range of
Audio
Frequenc
y
20 Hz to 20 kHz
Frequency Pitch

12. 12
AUDIBLE FREQUENCIESAUDIBLE FREQUENCIES
•This range decreases as we get older and our ears
lose their sensitivity to both high and low
frequencies.
•Animals have different ranges of audible frequencies.
Dogs and bats have a much higher upper audible
limit. Bats can produce and detect very high
ultrasonic sounds. This enables them to avoid
obstacles, even when flying in the dark.

13. 13
PITCHPITCH
•The pitch of a sound depends on its
frequency. The higher the frequency,
the higher the pitch.
•To obtain a note of higher pitch from a
vibrating string, we can
–increase the tension
–shorten the length
–use a thinner string of smaller mass per
unit length

14. 14
Compare the loudness of sound with
same frequency
louder sound with
greater amplitude
softer sound with
smaller amplitude
Louder musical notes can be
produced by hitting the
instruments harder so as to
produce vibrations of
greater amplitude.

15. 15
Loudness of sound
Loudness is related to the objective
quantity amplitude,
The larger the amplitude the
louder the sound.

16. 16
Noise
•Noise causes stress, fatigue,
headache and decreases
concentration. It makes
people more irritable and
aggressive.
•Prolonged exposure to
sounds exceeding 85 dBexceeding 85 dB can
permanently damage the
ears.
•Sounds exceeding 130dBexceeding 130dB
are above what the human
ear can withstand and may
result in serious pain and
permanent damage.

17. 17
LOUDNESSLOUDNESS
•If the volume control of a radio is suddenly
turned up, the sound suddenly becomes
very loud.
•The air particles in front of the speaker gain
more energy and begin to vibrate with
greater amplitude.
•The maximum displacement or amplitude
increases.

18. 18
LOUDNESSLOUDNESS
•The intensity or loudness of the sound has
increased.
•The unit for measuring noise level is the
decibel (dB). If the sound exceeds 80 dB, ear
protectors must be used to prevent
permanent ear damage.

19. 19
Noise and Music
Noise is sound with irregular waveform.
Musical note is sound with regular waveform.
sound from piano sound from violin

20. 20
Comparing sound waves and light waves
Feature Sound waves Light waves
transfer energy yes yes
can travel throughsolids, liquids and gases
but need a medium
vacuum, gases, some solid
and liquids, no medium
needed
speed 330 m/s in air
1500 m/s in water
5 000 m/s in steel
3 x 10
8
m/s in air
2.2 x 10
8
m/s in water

2 x 10
8
m/s in glass

type of wave longitudinal transverse
typical frequency
typical wavelength
1 kHz
10 cm or 1 m
5 x 10 Hz
5000 nm = 5 x 10
-7
m
part of the
electromagnetic
spectrum
no
yes

21. 21
Qus 3

22. 22
Qus 4

23. 23
Ultrasound

24. 24
Ultrasound

25. 25
RecapRecap
•What can you say about these sounds? What can you say about these sounds?
Which factors are Which factors are differentdifferent??
PitchPitch
LoudnessLoudness
QualityQuality
Pitch & LoudnessPitch & Loudness

26. 26
Resonance
•Principle.
•Play short clip on
glass breaking.
•Play clip on
resonance later
(glass).
•Bridges.

27. 27
•Tacoma Narrows bridge in Washington