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Standing waves on a \(1.0-\) m-long string that is fixed at both ends are seen at successive frequencies of \(24 \mathrm{Hz}\) and \(36 \mathrm{Hz}\) a. What are the fundamental frequency and the wave speed? b. Draw the standing-wave pattern when the string oscillates at \(36 \mathrm{Hz}\)

Short Answer

Expert verified
a. The fundamental frequency of the wave is 12 Hz and the wave speed is 24 m/s. b. The standing wave pattern at 36 Hz will consist of three antinodes and four nodes, including the nodes at the end points of the string.

Step by step solution

01

Calculate the Fundamental Frequency

The fundamental frequency (1st harmonic) can be found by subtracting the lower known frequency from the higher one as it represents the frequency difference between the first harmonic and the second harmonic. So, the fundamental frequency = 36Hz - 24Hz = 12Hz.
02

Calculate the Wave Speed

We know the wave speed (v) is given by the formula: v = fλ. Here, the fundamental frequency (f) is 12 Hz. In the case of the fundamental frequency (1st harmonic), the wavelength (λ) is twice the length of the string, which is 2m. Therefore, the wave speed v = 12 Hz * 2m = 24 m/s.
03

Draw Standing-Wave Pattern at 36 Hz

Knowing that the frequency of 36 Hz represents the third harmonic of the wave, there would be three antinodes (points that undergo maximum displacement) and four nodes (points with no displacement) on the string. Draw them evenly spaced along the string with an amplitude representing the maximum vertical displacement from rest position. Also, nodes should be at the fixed ends of the string.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Harmonics
Harmonics are the integral multiples of the fundamental frequency of a system, describing the different standing wave patterns that can form on a medium such as a string or an air column. When you pluck a string, it can vibrate in different patterns, producing different harmonics.

* **Fundamental Frequency (1st Harmonic)**: It's the lowest frequency at which a string vibrates, creating a standing wave pattern with a single antinode and nodes at the ends.
* **2nd Harmonic**: This involves a standing wave pattern that includes one more node and antinode, with double the fundamental frequency.
* **3rd Harmonic**: At this stage, the string forms three distinct antinodes and has a frequency three times that of the fundamental frequency. As noted in the original exercise, a frequency of 36 Hz, which is three times the fundamental frequency of 12 Hz, corresponds to the third harmonic. The pattern for this will display three loops, indicating three antinodes.

These harmonics and their respective frequencies help in understanding the succession of patterns formed as the frequency increases. They are essential in musical instruments where the quality of sound is richer due to multiple harmonics being heard at once.
Wave Speed
Wave speed measures the rate at which the wave propagates through a medium. In a string fixed at both ends, the wave speed is determined by both the tension in the string and the mass density of the string. Interestingly, wave speed remains constant for a given medium and conditions, regardless of frequency.

Wave speed is calculated using the formula:
\[ v = f \times \lambda \]
where \( v \) is the wave speed, \( f \) is the frequency, and \( \lambda \) is the wavelength of the wave.

The frequency specifically refers to how many cycles occur per second, measured in hertz (Hz). Wavelength, on the other hand, is the physical length of one cycle of the wave. The fundamental wavelength in a string fixed at both ends is twice the length of the string, as the wave has to return to its starting point to complete one full cycle.

In the problem given, we've determined the wave speed to be 24 m/s using a frequency of 12 Hz and a wavelength of 2 meters.
Fundamental Frequency
The fundamental frequency, often called the first harmonic, is the lowest frequency at which a system resonates. Imagine a string of a musical instrument; when plucked, it vibrates at this fundamental frequency to produce the basic note.

To find the fundamental frequency, one can analyze the differences between known consecutive harmonics. For instance, in the original exercise, the frequencies were 24 Hz (second harmonic) and 36 Hz (third harmonic). The difference between these frequencies, 12 Hz, gives us the fundamental frequency.

It's essential for understanding how different standing waves and harmonics derive from a simple frequency. This knowledge helps in tuning musical instruments and understanding wave behaviour in various mediums.

By knowing the fundamental frequency, other harmonics and their respective standing wave patterns can be predicted accurately, making it a crucial concept in wave mechanics and acoustics.

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Most popular questions from this chapter

A \(1.0-\) m-tall vertical tube is filled with \(20^{\circ} \mathrm{C}\) water. A tuning fork vibrating at \(580 \mathrm{Hz}\) is held just over the top of the tube as the water is slowly drained from the bottom. At what water heights, measured from the bottom of the tube, will there be a standing wave in the tube above the water?

Two strings are adjusted to vibrate at exactly \(200 \mathrm{Hz}\). Then the tension in one string is increased slightly. Afterward, three beats per second are heard when the strings vibrate at the same time. What is the new frequency of the string that was tightened?

A soap bubble is essentially a very thin film of water \((n=\) 1.33) surrounded by air. The colors that you see in soap bubbles are produced by interference, much like the colors of dichroic glass. a. Derive an expression for the wavelengths \(\lambda_{\mathrm{c}}\) for which constructive interference causes a strong reflection from a soap bubble of thickness \(d\) Hint: Think about the reflection phase shifts at both boundaries. b. What visible wavelengths of light are strongly reflected from a 390 -nm- thick soap bubble? What color would such a soap bubble appear to be?

Two loudspeakers in a plane, 5.0 apart, are playing the same frequency. If you stand \(12.0 \mathrm{m}\) in front of the plane of the speakers, centered between them, you hear a sound of maximum intensity. As you walk parallel to the plane of the speakers, staying \(12.0 \mathrm{m}\) in front of them, you first hear a minimum of sound intensity when you are directly in front of one of the speakers. a. What is the frequency of the sound? Assume a sound speed of \(340 \mathrm{m} / \mathrm{s}\) b. If you stay \(12.0 \mathrm{m}\) directly in front of one of the speakers, for what other frequencies between \(100 \mathrm{Hz}\) and \(1000 \mathrm{Hz}\) is there a minimum sound intensity at this point?

What is the thinnest film of \(\mathrm{MgF}_{2}(n=1.39)\) on glass that produces a strong reflection for orange light with a wavelength of \(600 \mathrm{nm} ?\)

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