The auto focus camera uses an ultrasonic sound wave to focus on subjects. The camera sends sound waves, which bounce off distant objects and return to the camera. The sensor determines the time it takes for the waves to return and then determines the distance the object is from the camera.

Calculate the frequency and wavelength of the annoying sound made by a mosquito when it beats its wings with average speed 600 wing bits per second. Let us assume that the speed of sound waves is 344 m s -1. How does cutting the frequency of a wave source by half affect the speed of the waves?

Assuming the speed of sound in air is 344 m s -1, calculate the wavelength of sound corresponding to the upper range of audible hearing. Assuming the speed of sound in air is 344 m s -1, calculate the wavelength of this infrasonic sound wave made by an elephant.

The ship sends a signal to determine the depth of the ocean. The signal returns after 2.5 seconds. Waves and medium moving in the same direction. The distance between successive wave points that are in phase. How often one wavelength passes.

Half the difference between the high points and low points of the waves. The distance over which a wave propagates in a time interval. The time it takes for one wavelength to pass a point. At the end of this section, you will be able to. Describe how the sound disturbances generated inside open and closed tubes change the characteristics of the sound and how this applies to the sounds produced by musical instruments.

• Identify antinodes, nodes, fundamentals, overtones and harmonics.
• Identify instances of sound interference in everyday situations.
• Calculate the tube length using sound wave measurements.

Interference is a sign of waves, all of which exhibit constructive and destructive interference exactly like those seen with water waves. In fact, one way to prove that something "is a wave" is to observe interference effects. So sound, which is a wave, we expect it to interfere; we have already mentioned some of these effects, such as beats of two similar notes played at the same time.

Figure 2 shows the clever use of sonic interference to cancel noise. Larger applications of active noise abatement through destructive interference are envisioned for entire passenger compartments on commercial aircraft. To obtain destructive interference, a quick electronic analysis is performed and a second sound is introduced with its maxima and minima, which are completely canceled out from the incoming noise. Sound waves in liquids are pressure waves and are consistent with Pascal's principle; pressures from two different sources are added and subtracted like prime numbers; that is, the positive and negative calibration pressures are added to a much lower pressure, producing a sound of lesser intensity.

Although completely destructive interference is possible only in the most basic environments, noise levels can be reduced by 30 dB or more with this technology. Designed to cancel noise with destructive interference, headphones create a sound wave that is exactly the opposite of the incoming sound. These headphones can be more effective than the simple passive attenuation used in most protective headphones.

Where else can we observe sound interference? All sound resonances, for example in musical instruments, are caused by constructive and destructive disturbances. Only resonant frequencies constructively interfere with the formation of standing waves, while others prevent destruction and are absent. From the horns made to blow over a bottle, to the distinctive aroma of a violin's soundbox, to the recognizability of a great singer's voice, resonant and standing waves play a vital role.

Interference is such a fundamental aspect of waves that observing interference is proof that something is a wave. The wave nature of light has been established by experiments showing interference. Similarly, when electrons scattered from crystals exhibited interference, their wave nature was confirmed exactly as predicted by symmetry with some of the wave characteristics of light.

Suppose we hold the tuning fork near the end of the tube, which is closed at the other end, as shown in figure 3, fig. 4, fig. 5 and figure. If the tuning fork is at just the right frequency, the air column in the tube resonates loudly, but at most frequencies it vibrates very little. This observation simply means that the air column only has certain natural frequencies. The numbers show how the resonance is formed at the lowest of these natural frequencies. The disturbance travels down the tube at the speed of sound and bounces off the closed end.

If the tube is just the right length, the reflected sound returns to the tuner plug exactly half a cycle later, and it interferes constructively with the ongoing sound produced by the tuning fork. The incoming and reflected sounds form a standing wave in the tube, as shown.

A standing wave formed in a pipe has a maximum air displacement at the open end, where movement is not restricted, and a displacement at the closed end, where air movement is stopped. This same resonance can be caused by vibration introduced at or near the closed end of the tube, as shown in the figure.

It is best to consider this the natural vibration of the air column, regardless of its induction. The same standing wave is created in the pipe by vibration introduced near its closed end. Another resonance for a tube closed at one end. It has maximum air displacements at the open end, and none at the closed end. This high frequency vibration is the first overtone.

Considering that maximum air displacements are possible at the open end, and none at the closed end, other shorter wavelengths, such as those shown in the figure, can occur in the pipe. Continuing this process, a whole series of shortwave and high frequency sounds are found that resonate in the tube. We use specific terms for resonances in any system. The lowest resonant frequency is called the fundamental, and all higher resonant frequencies are called overtones.

All resonant frequencies are integer multiples of the fundamental, and they are collectively called harmonics. The fundamental is the first harmonic, the first overtone is the second harmonic, and so on. Figure 9 shows the fundamental and first three overtones in a pipe closed at one end.

Fundamental and three lower overtones for a tube closed at one end. All have maximum air displacements at the open end and no closed end. Fundamental and overtones can be present simultaneously in many combinations. The fundamental frequency is the same, but the overtones and their combination of intensities are different and subject to obscuring the musician. This mix is ​​what gives different musical instruments their distinctive characteristics, whether they have air columns, strings, sound boxes, or drum heads.

In fact, much of our speech is determined by the formation of the cavity formed by the throat and mouth and the positioning of the tongue to correct the fundamental and combination of overtones. For example, simple resonant resonators can resonate with the sound of vowels.

In boys, during puberty, the larynx grows and the shape of the resonant cavity changes, which leads to a difference in the prevailing frequencies in speech between men and women. The throat and mouth form an air column, closed at one end, which resonates in response to vibrations in the voice box. The spectrum of overtones and their intensity vary with the shape of the mouth and tongue to form different sounds. The voice box can be replaced with a mechanical vibrator and intelligible speech is still possible.