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For a string stretched between two supports, two successive standing-wave frequencies are \(525 \mathrm{~Hz}\) and \(630 \mathrm{~Hz}\). There are other standing-wave frequencies lower than \(525 \mathrm{~Hz}\) and higher than \(630 \mathrm{~Hz}\). If the speed of transverse waves on the string is \(384 \mathrm{~m} / \mathrm{s},\) what is the length of the string? Assume that the mass of the wire is small enough for its effect on the tension in the wire to be ignored.

Short Answer

Expert verified
The length of the string is 1.83 m.

Step by step solution

01

Find the Difference of Frequencies

Calculate the difference between the two given frequencies. That is \(\Delta f = f_2 - f_1 = 630Hz - 525Hz = 105Hz\)
02

Calculate the Fundamental Frequency using the difference

As described above, these frequencies are an overtone that means they are integral multiples of a fundamental frequency. So, the fundamental frequency i.e., the frequency corresponding to the fundamental mode or first overtone is equal to the difference in frequencies. So, \(f_1 = \Delta f = 105Hz\).
03

Determine the Wavelength

The wavelength (\(\lambda_1\)) of the wave corresponding to the fundamental frequency can be calculated using the wave speed equation \(v = f \lambda\), where \(v\) is the wave speed, \(f\) is its frequency, and \(\lambda\) is the wavelength. Rearranging it, we get \(\lambda_1 = \frac{v}{f_1} = \frac{384 m/s}{105Hz} = 3.657 m\)
04

Find the Length of the String

Now, remember that for a fundamental mode (first overtone), the length of the string is equal to half of the wavelength. Hence, length of the string \(L = \frac{\lambda_1}{2} = \frac{3.657 m}{2} = 1.83 m\)

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Key Concepts

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

Fundamental Frequency
Understanding the fundamental frequency is crucial for mastering the concept of standing waves, particularly in the context of musical instruments and the physics of sound. The fundamental frequency, often referred to as the 'first harmonic' or the 'first overtone', is the lowest frequency produced by a vibrating object, like a string or air column. It represents the simplest form of vibration, with the wavelength being the largest compared to all other harmonics.

Imagine plucking a guitar string; the sound you hear is a complex mixture of various frequencies. The pitch you recognize is usually the fundamental frequency. This is the tone that determines the musical note of the string. Higher frequencies, called harmonics or overtones, are whole-number multiples of this fundamental frequency and add to the timbre of the note. In the context of standing waves on a string, the string vibrates in segments, with nodes (points of no movement) and antinodes (points of maximum movement). For the fundamental frequency, there's just one segment – that's one antinode between the two ends of the string. In the exercise provided, we determined the fundamental frequency by calculating the difference between two successive standing wave frequencies.
Wave Speed Equation
The relation between wave speed, frequency, and wavelength is foundational in understanding wave dynamics. To solve many physics problems involving waves, we use the wave speed equation \( v = f \lambda \), where \( v \) is the wave speed, \( f \) is the frequency of the wave, and \( \lambda \) represents the wavelength. This simple yet mighty equation connects these three core properties of waves.

It's worth noting that the wave speed \( v \) is determined by the medium through which the wave travels and typically remains constant for a given medium under the same conditions. Thus, changes in frequency directly affect the wavelength and vice versa. When we look at standing waves on a string, the tension and mass of the string, as well as its length, influence wave speed. In our exercise, we used the wave speed equation to find the wavelength corresponding to the fundamental frequency, which we then used to calculate the length of the string.

Through understanding the wave speed equation, one can predict how a change in one variable affects the others, which is vital for tuning musical instruments, designing acoustic spaces, and even in modern technological applications involving wave phenomena.
Transverse Waves
Transverse waves are a type of wave where the disturbance moves perpendicular to the direction of the wave's advance. This is best visualized with a string or a slinky: When you move one end up and down, you create peaks (crests) and valleys (troughs) that move along the length of the object. The parts of the string that are momentarily stationary are called nodes, while the highest and lowest points are known as antinodes. Transverse waves are everywhere, from ripples on a pond to electromagnetic waves like light.

The exercise we've been discussing involves transverse waves on a string. These waves are fundamental for musical instruments that use strings, like guitars, violins, and pianos. For strings with both ends fixed, as in the exercise, certain frequencies will produce standing waves - patterns of vibration that combine to look like they're standing still. The frequencies that create these patterns are intimately linked to the length of the string and are vital for producing the different notes we hear in music. Recognizing this connection between transverse waves and music is not only fascinating but adds a rich layer of understanding when learning about wave motion and sound production.

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Most popular questions from this chapter

The speed of sound in air at \(20^{\circ} \mathrm{C}\) is \(344 \mathrm{~m} / \mathrm{s}\). (a) What is the wavelength of a sound wave with a frequency of \(784 \mathrm{~Hz}\), corresponding to the note \(\mathrm{G}_{5}\) on a piano, and how many milliseconds does each vibration take? (b) What is the wavelength of a sound wave one octave higher (twice the frequency) than the note in part (a)?

Energy Output. By measurement you determine that sound waves are spreading out equally in all directions from a point source and that the intensity is \(0.026 \mathrm{~W} / \mathrm{m}^{2}\) at a distance of \(4.3 \mathrm{~m}\) from the source. (a) What is the intensity at a distance of \(3.1 \mathrm{~m}\) from the source? (b) How much sound energy does the source emit in one hour if its power output remains constant?

The wave function of a standing wave is \(y(x, t)=(4.44 \mathrm{~mm})\) \(\sin [(32.5 \mathrm{rad} / \mathrm{m}) x] \sin [(754 \mathrm{rad} / \mathrm{s}) t] .\) For the two traveling waves that make up this standing wave, find the (a) amplitude; (b) wavelength; (c) frequency; (d) wave speed; (e) wave functions. (f) From the information given, can you determine which harmonic this is? Explain.

A fisherman notices that his boat is moving up and down periodically, owing to waves on the surface of the water. It takes \(2.5 \mathrm{~s}\) for the boat to travel from its highest point to its lowest, a total distance of \(0.53 \mathrm{~m} .\) The fisherman sees that the wave crests are spaced \(4.8 \mathrm{~m}\) apart. (a) How fast are the waves traveling? (b) What is the amplitude of each wave? (c) If the total vertical distance traveled by the boat were \(0.30 \mathrm{~m}\) but the other data remained the same, how would the answers to parts (a) and (b) change?

A strong string of mass \(3.00 \mathrm{~g}\) and length \(2.20 \mathrm{~m}\) is tied to supports at each end and is vibrating in its fundamental mode. The maximum transverse speed of a point at the middle of the string is \(9.00 \mathrm{~m} / \mathrm{s}\) The tension in the string is \(330 \mathrm{~N}\). (a) What is the amplitude of the standing wave at its antinode? (b) What is the magnitude of the maximum transverse acceleration of a point at the antinode?

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