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A piano tuner stretches a steel piano wire with a tension of 800 N. The steel wire is 0.400 m long and has a mass of 3.00 g. (a) What is the frequency of its fundamental mode of vibration? (b) What is the number of the highest harmonic that could be heard by a person who is capable of hearing frequencies up to 10,000 Hz?

Short Answer

Expert verified
(a) 408.25 Hz; (b) 24th harmonic.

Step by step solution

01

Convert Units

The mass of the wire is given in grams and must be converted to kilograms for our calculations since the standard unit of mass in physics is the kilogram. Therefore, we convert 3.00 g to kg:3.00g=0.003kg
02

Calculate Linear Mass Density

Next, we determine the linear mass density (μ) of the wire, which is mass per unit length. It's given by the formula:μ=mLWhere:- m=0.003kg (mass of the wire)- L=0.400m (length of the wire)Substituting the values:μ=0.0030.400=0.0075kg/m
03

Calculate Speed of Wave on Wire

The speed of the wave on the string v is calculated using the formula:v=TμWhere:- T=800N (tension)- μ=0.0075kg/m (linear mass density)v=8000.0075326.60m/s
04

Calculate Fundamental Frequency

The fundamental frequency f of a stretched string is given by the formula:f=v2LSubstitute the values we have:f=326.602×0.400408.25Hz
05

Determine the Highest Audible Harmonic

To find the highest harmonic number n that can be heard (10,000Hz), use the relation:fn=n×f10,000Using the fundamental frequency f=408.25Hz:n10,000408.2524.50Since n must be an integer, the highest harmonic is 24.

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Key Concepts

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

Harmonics
Harmonics are fascinating phenomena observed with vibrating systems like strings and air columns. They occur when a wave can exist at multiple frequencies that are integer multiples of a fundamental frequency. The fundamental frequency is often the lowest frequency and the first harmonic. On a musical string instrument, this represents the base note you hear, while the higher harmonics contribute to the instrument's timbre, providing richness and depth to the sound.

Understanding harmonics is key because it helps us calculate higher frequencies that a vibrating object can produce. For a wire or string, each harmonic increases in frequency by whole number multiples. If the wire's fundamental frequency is 408.25 Hz, the next harmonic (the second harmonic) would be twice this frequency, and so on. This is particularly useful in music to help understand notes and their octaves. Learn about harmonics, and you'll better appreciate how musicians can produce a range of notes with just a few strings or instruments.
Linear Mass Density
Linear mass density is the mass of a wire or string divided evenly along its length. It's denoted by the Greek letter μ (mu) and has the units of kilograms per meter (kg/m). This measure is crucial when examining how a string vibrates, as it affects both the tension and the wave speed.

In the example exercise, we calculated the linear mass density of a piano wire by dividing the total mass (0.003 kg) by its length (0.400 m), resulting in 0.0075 kg/m. This density is important because it directly influences the string's wave speed and, subsequently, the frequencies of the harmonics it can produce. In musical terms, the linear mass density affects which notes are heard and their pitch. Thicker or denser strings typically have lower pitches, while lighter, less dense strings tend to have higher pitches.
Wave Speed
Wave speed on a string or wire is a pivotal concept when considering vibrations and sound. It can be calculated using the tension in the string and its linear mass density. The formula to determine wave speed is:
  • v=Tμ
  • where v is the wave speed, T is the string tension, and μ is the linear mass density.

In our exercise, with a tension of 800 N and a linear mass density of 0.0075 kg/m, we computed the wave speed as approximately 326.60 m/s. This speed guides how quickly waves or vibrations travel along the string. Faster wave speeds lead to higher frequency sounds. Understanding wave speed is essential for tuning string instruments, designing musical instruments, and any applications involving waves and vibrations, including engineering and multimedia fields. Wave speed, in the context of sound, influences how far and how fast sound can travel, impacting both musical acoustics and communication systems.

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Most popular questions from this chapter

An ant with mass m is standing peacefully on top of a horizontal, stretched rope. The rope has mass per unit length μ and is under tension F. Without warning, Cousin Throckmorton starts a sinusoidal transverse wave of wavelength λ propagating along the rope. The motion of the rope is in a vertical plane. What minimum wave amplitude will make the ant become momentarily weightless? Assume that m is so small that the presence of the ant has no effect on the propagation of the wave.

A wire with mass 40.0 g is stretched so that its ends are tied down at points 80.0 cm apart. The wire vibrates in its fundamental mode with frequency 60.0 Hz and with an amplitude at the antinodes of 0.300 cm. (a) What is the speed of propagation of transverse waves in the wire? (b) Compute the tension in the wire. (c) Find the maximum transverse velocity and acceleration of particles in the wire.

You must determine the length of a long, thin wire that is suspended from the ceiling in the atrium of a tall building. A 2.00-cm-long piece of the wire is left over from its installation. Using an analytical balance, you determine that the mass of the spare piece is 14.5 μg. You then hang a 0.400-kg mass from the lower end of the long, suspended wire. When a small-amplitude transverse wave pulse is sent up that wire, sensors at both ends measure that it takes the wave pulse 26.7 ms to travel the length of the wire. (a) Use these measurements to calculate the length of the wire. Assume that the weight of the wire has a negligible effect on the speed of the transverse waves. (b) Discuss the accuracy of the approximation made in part (a).

A light wire is tightly stretched with tension F. Transverse traveling waves of amplitude A and wavelength λ1 carry average power Pav,1=0.400 W. If the wavelength of the waves is doubled, so λ2=2λ1, while the tension F and amplitude A are not altered, what then is the average power Pav,2 carried by the waves?

A transverse wave on a rope is given by y(x,t)=(0.750cm)cos π[(10.400cm1)x+(250s1)t] (a) Find the amplitude, period, frequency, wavelength, and speed of propagation. (b) Sketch the shape of the rope at these values of t: 0, 0.0005 s, 0.0010 s. (c) Is the wave traveling in the +x or x-direction? (d) The mass per unit length of the rope is 0.0500 kg/m. Find the tension. (e) Find the average power of this wave.

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