Answer to sound worksheet
1a.
Compressions are regions where air particles are closer together; the air pressure
in these regions is greater than the surroundings. Rarefactions are regions where
air particles are further apart; the air pressure in these regions is lower than the
surroundings.
1b.
600/2 = 300 mm
1c.
550
2a.
Vibrations of the cone cause air layers next to it to vibrate, this in turns vibrates
subsequent air layers. These vibrations set up a series of compressions and
rarefactions, hence sound energy is transmitted through the air to the microphone.
2b
(i) v = fλ = 200 ( 6.8/4) = 340 m/s
(ii) 6.8 /(340/2.0) = 0.04
(iii) Sound becomes lower in pitch as frequency is changing from 200 Hz to 20
Hz. From 20 Hz to 2 Hz, no sound can be heard.
3.
Dog’s whistle produces a sound with a frequency higher than the audile frequency
of human.
4.
No sound will be transmitted because sound cannot travel through a vacuum.
5.
Sound travels faster in solid than in air, so people are able to detect approaching
enemy faster.
6a.
d = s x t = 330 x 3 = 990 m
6b.
Speed of light is instantaneous; time taken for light to travel is negligible.
Factors : humidity; wind, reaction time, etc
7.
v = d/t = 30/(0.040/2) = 1500 m/s
8a.
f = (50 x 600)/60 = 500 Hz
8b.
v = fλ
λ = 340/500 = 0.68 m
9a
There is an unknown peak in between the two sound waves.
9b.
d = v x t = 4000 x 10 x 10-6 = 0.04 m
9c.
Gamma rays pose health risk to the user.
10a
(i) Diagram (ii) because it has a lower frequency
(ii) Diagram (ii) because it has a higher amplitude
10b.
Quality of sound produced differ as waveforms are different.
11a.
When the loudspeaker was switched on, the air layers in-front of the loudspeaker
were set in vibration parallel to the direction of the sound wave. A series of
compression and rare-fraction were set up in the air. Hence the candle flame
would be set in vibration according to the frequency of the sound.
11b.
When the vacuum pump was switched on, the vibration of the candle flame
reduces and at the same time, the sound produced by the loudspeaker became
softer.
11c.
Transmission of sound requires a medium.
12.
When someone inhales helium, their voice becomes very high pitched, and they
sound like cartoon characters. This is because helium is much less dense than air,
and the velocity of sound, which depends on density of the medium, is much
greater in helium. The wavelengths of the standing waves supported by the
resonance chambers is the same, so the greater speed means a greater frequency
(v= f×) and hence a higher pitched sound. The speed of sound depends on two
factors: elasticity and density. The more elastic a medium, the greater the speed.
The more dense the medium the slower the speed of sound. For example steel is
6000 times more dense than air but 2,000,000 times more elastic than air, so
sound travels 16 times faster in steel than in air.
13a
v = fλ
λ = 340/1000 = 0.34 m
13b. Change in wave length, Δλ Speed of the moving source of waves, v
-------------------------------- = ------------------------------------------------Original wavelength , λ
Speed of waves in medium, c
Δλ = 0.025 m
Λ = 0.365 m
13c.
v = fλ
f = 932 Hz
14.