In this homework, you will be using a sound simulation. It\'s available online f

Question

In this homework, you will be using a sound simulation. It's available online from the class homepage: http://phet.colorado.edu/simulations/sims.php?sim=Sound. Begin by running the Sound Applet and exploring the various controls you have: You can change amplitude and frequency of the sound wave. You can move the listener toward or away from the speaker. You can turn the audio on or off, and you can listen to either the sound at the speaker or the sound heard by the listener. You can switch between the Listen Screen and the Measure Screen (you can ignore the other Screens for this assignment.) In the Measure Screen you have a ruler and timer which you can use to make measurements; you also have blue lines which you can move around to help you measure. You can stop, run, or advance frame by frame the sound waves. The Listen Screen of the sim lets you adjust the frequency and amplitude sliders and move the listener. The solid gray of the background represents the pressure of the air when no sound wave is present. Use the adjustments available to closely examine the relationship between the movement of the speaker cone and the sound waves produced and traveling away from the cone. After playing for a bit, come back here and decide whether each of the following statements are T-True, or F-False. (If the first is T and the rest are F, enter TFFFF) A) To produce a lower pitch tone, the speaker must oscillate back and forth fewer times each second. B) To increase the volume of a tone at 400 Hz heard by the listener, the speaker must oscillate back and forth fewer times each second than it does to produce the tone with lower volume. C) If the speaker produces larger fluctuations in pressure, the volume of the tone heard by the listener increases. D) In this simulation, a darker shade of gray indicates an increase in pressure compared to the undisturbed air pressure. E) When the speaker is producing sound waves, the motion of the speaker produces a slight increase in the pressure in front of the speaker during the forward motion of the speaker head and a slight decrease in pressure during the backward motion of the speaker head.

Explanation / Answer

A) False. I determined this by observing that when I change the frequency slider, the rate at which the speaker cone oscillates changes and the pitch I heard also changes. When I decreased the frequency, the speaker oscillated fewer times per second and the pitch of the tone was lower.

B)   False. I determined this by playing with the frequency and amplitude controls. When I change the frequency slider, the rate at which the speaker cone oscillates changes and the pitch I heard also changes. When I decreased the frequency, the speaker oscillated fewer times per second and the pitch of the tone was lower. Changing the rate at which the speaker oscillated never changed the volume heard by the listener.

C) True. I determined this by increasing the amplitude with the slider control with the sound playing as heard by the listener, and observed that the shading of the sound wave developed higher contrast (corresponding to higher pressure fluctuations) and the sound got louder.

D) True. I determined this by looking at the last panel of the simulation, where the air pressure can be reduced to zero by removing all the air from the jar. As the air pressure decreased, the shading inside the jar became a darker gray.

E) False. From the earlier part of this question, I determined that a lighter shade of gray corresponds to an increase in pressure, and I observed that when the speaker moves forward the shade of gray in front of it gets lighter. Therefore when the speaker moves forward it produces a slight increase in pressure.

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