Consider this passage from a hypothetical 10th grade textbook.
Airplane passengers hate the loud noise produced by airplane engines. Like all sound waves, these noises travel at about 340 meters per second. When they reach your ear, the sound waves make your ear drum vibrate.
Some airlines have started experimenting with anti-sound headphones. These headphones contain speakers that give off "anti-sound" waves. The anti-sound waves are designed to cancel out the sound waves coming from the engines. As a result, the passenger hears softer engine noise. Early testing shows that these anti-sound headphones work fairly well.

1. | Anti-sound headphones reduce the noise level heard by the passenger primarily by taking advantage of:

A. | Absorption

B. | Standing waves

C. | Interference

D. | Diffraction

2. | In air at 20° C, lower-frequency sound waves travel 340 meters per second. In air at 20° C, higher-frequency sound waves travel:

A. | More than 340 meters per second

B. | About 340 meters per second

C. | Fewer than 340 meters per second

D. | We cannot determine the answer.

3. | From the passage, we can infer that an anti-sound headphone cannot work unless it incorporates some

A. | Absorbing surfaces to "soak up" excess sound from the engines

B. | Small fans to circulate air near the passenger's ears

C. | Reflecting surfaces to redirect sound from the engines

D. | Microphones to detect sound from the engines.

4. | When sound waves of wavelength 0.34 m enter your ears, what is the approximate period of oscillation of your ear drums, in seconds?

A. | 1000

B. | 100

C. | .01

D. | .001

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