Airplane passengers hate the loud noise produced by airplane engines. Like all s

Question

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.

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

In air at 20

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

Explanation / Answer

1. C. Interference:

Explanation :
More appropriately, this is termed as Destructive Intereference. The headphone's sound waves are 180 degrees out of phase with the intruding waves from the airplane's engine. The two waves have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out, and the listener can focus on the sounds without getting disturbed.

2. B. About 340m/sec

Explanation: The dependence of speed of sound on frequency and pressure are normally insignificant in practical applications. In dry air, the speed of sound increases by about 0.1 m/s as the frequency rises from 10 Hz to 100 Hz.

3. D. Microphones to detect sound from engines.

Explanation: A microphone placed inside the ear cup "listens" to external sounds that cannot be blocked passively. Then the noise canceling circuitry senses the input from the microphone and generate a "fingerprint" of the noise, noting the frequency and amplitude of the incoming wave and creates a new wave that is 180 degrees out of phase with the waves associated with the noise.

4. D. 0.001 s

velocity=frequency* wavelength

340m/s= f * 0.34m

f=1000 Hz

hence Time period=1/frequency

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