Passage 7: Sound
Sound is critically important in marine ecosystems as a method of communication
for animals, submarines, and other technological instruments. Researchers
conducted an experiment to study sound waves in various aquatic contexts, with a
special focus on the speed of sound across varying media.
A speaker emitting high-frequency sound was utilized to generate sound waves at
a fixed frequency. Hydrophones, strategically placed at varying distances from the
radio, measured sound intensity and speed in freshwater, salt water, and air.
The first phase of experimental data collection involved measuring the speed of
sound in these three media at the same temperature. Results showed that there
was a significant difference between all three, with the most significant difference
between either water medium and air. Next, researchers varied the temperature
and salinity of the water in the tanks, measuring the speed of sound at regular
increments.
They also used ultrasound waves to map the seafloor, detecting obstacles. Findings
are tabulated in Table 1:
Attenuation in signal intensity was attributed to absorption and scattering of waves
in the water (as signal intensity decreased with increasing depth). Background noise
in the water column affected the precision of the measurements; regions with high
biological activity reduced measurement accuracy.
An ideal gas enclosed in a cylinder with a movable piston is initially at a
temperature of 300K and a pressure of 1.0 atm. It undergoes isothermal
expansion to twice the initial volume, and is then compressed isobarically until
reaching its original volume (Scenario 1).
Compare this to another scenario in which the same gas undergoes the same
isothermal expansion to twice its original volume but is then compressed
adiabatically to its original volume (Scenario 2).
Which of the following statements regarding this comparison is correct?
A) The final temperature of Scenario 1 is higher than Scenario 2
B) The final temperature of Scenario 1 is lower than Scenario 2
C) The final temperature of Scenario 1 is the same as Scenario 2
D) The final temperature of Scenario 2 is lower than the initial temperature of
300K
Correct answer: B. In both scenarios, the gasses undergo isothermal
expansion, meaning that the temperature remains constant at 300K. According to
Boyle’s Law (P1V1 = P2V2), this means that the pressure decreases accordingly in
both cases.
Scenario 1 (Isobaric compression): The gas is compressed at a constant pressure
to its original volume. Following the ideal gas law PV = nRT, if volume decreases and
pressure is constant, temperature must also decrease.
Scenario 2 (Adiabatic compression): The gas is compressed without any heat
exchange with surroundings. This means that both pressure and temperature must
increase because work is done on the gas; no heat is lost to the surroundings.
This means that the gas will have a higher temperature than the initial 300 K after
compression.
Thus, the correct answer states that the final temperature following isobaric
compression will be lower than the final temperature of adiabatic compression.
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