Page 27 - Physics 10_Float

SOUND

 Lift the pipe on the right vertically to a small height
and observe what happens.

Screen
For your information
Angle of Angle of reflection
incidence Wall Wave on
screen
Microphone
Pipe Table
Clock i r
Ear Amplifier Oscilloscope
By using an oscilloscope, you
can “see” sound waves.
Fig. 11.10: Reflection of sound

11.4 SPEED OF SOUND
Table 11.1
Speed of sound in various
Sound waves can be transmitted by any medium containing media
-1
particles that can vibrate. They cannot pass through vacuum. Medium Speed (m s )
Gases
However, the nature of the medium will affect the speed of
o
Air(0 C) 331
the sound waves. In general, the speed of sound in a liquid is Air (25 C) 346
0
five times that in gases; the speed of sound in solid is about Air(100 C) 386
o
o
fifteen times that in gases. The speed of sound in air is Hydrogen (0 C) 1290
o
affected by changes in some physical conditions such as Oxygen (0 C) 317
o
temperature, pressure and humidity etc. Helium (0 C) 972
0
-1
The speed of sound in air is 343 m s at one atmosphere of Liquids at 25 C
Distilled water 1498
pressure and room temperature (21°C). The speed varies Sea water 1531
0
with temperature and humidity. The speed of sound in solids Solids 25 C
and liquids is faster than in air. Following relation can be used Wood 2000
Aluminium 6420
to find the speed of sound:
Brass 4700
v = f λ ........ (11.6) Nickel 6040
Iron 5950
where v is the speed, f is the frequency and λ is the Steel 5960
wavelength of sound wave. Flint Glass 3980
Example 11.2: Calculate the frequency of a sound wave of
-1
speed 340 m s and wavelength 0.5 m.
-1
Solution: Given that; speed of waves v = 340 m s

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