UNIT 8

A rope stretched between two fixed points can support transverse standing waves. What is the ratio of the sixth harmonic frequency to the third harmonic frequency?

2

You are standing on a railroad track as a train approaches at a constant velocity. Suddenly the engineer sees you, applies the brakes, and sounds the whistle. Which of the following describes the sound of the whistle as you hear it starting from that moment?

Loudness increasing, pitch decreasing

A tube with one end closed and one end open resonates for a wave with wavelength la as shown. The next shorter wavelength at which resonance will occur is lb. The ratio of these two wavelengths la / lb is

5/3

A pair of protective headphones reduces the sound of a jet engine from 140 dB to 110 dB. What percent of the noise is being blocked?

99.9%

In which of the following situations involving a source of sound and a detector of the sound is it possible that there is NO perceived Doppler shift?

Both the source and detector travel in the same direction.

Sound waves travel at 350 m/s through warm air and at 3500 m/s through brass. What happens to the wavelength of a 700 Hz acoustic wave as it enters brass from warm air?

It increases by a factor of 10

A musician plucks a string on an acoustic guitar. Standing waves will most likely occur in which of the following media?

The guitar string The air inside the guitar

A sound wave with frequency f travels through air at speed v. With what speed will a sound wave with frequency 4f travel through the air?

V

A sound wave travels through a metal rod with wavelength l and frequency f. Which of the following is true?

When this sound wave passes into air, the wavelength will change While in the metal rod, the l. and frequency f have an inverse relationship

An alarm whose frequency is 400 Hz is dropped out of a third-floor window. The student who drops it measures the frequency with a very sensitive oscilloscope. The measured frequency

appears lower than 400 Hz and the frequency decreases as it falls

A beam of monochromatic light entering a glass window pane the air will experience a change in

speed and wavelength