Math Problem Statement

One of the ‘strings’, or wires on a piano is tuned to middle C, at 262 Hz. tension T = 750 N, and has a mass per unit length, μ = 3.4×10. what is the wave speed on this string, and what length should it be for middle C to be the fundamental frequency? A second instrument uses a pipe, closed at one end and open at the other, to produce middle C as the fundamental frequency from the vibrations of the air in the tube. What length would this tube need to be?

Solution

To solve this problem, we will calculate the wave speed on the piano string, the length of the string for the fundamental frequency, and the length of the closed-open pipe that produces the same fundamental frequency.


Part 1: Wave Speed on the Piano String

The wave speed vv on a string is determined using the formula:

v=Tμv = \sqrt{\frac{T}{\mu}}

Where:

  • T=750NT = 750 \, \text{N} (tension),
  • μ=3.4×103kg/m\mu = 3.4 \times 10^{-3} \, \text{kg/m} (mass per unit length).

v=7503.4×103v = \sqrt{\frac{750}{3.4 \times 10^{-3}}}

v=220588.24469.62m/sv = \sqrt{220588.24} \approx 469.62 \, \text{m/s}


Part 2: Length of the String for Fundamental Frequency

The fundamental frequency ff for a string is given by:

f=v2Lf = \frac{v}{2L}

Rearranging to find the length LL:

L=v2fL = \frac{v}{2f}

Substitute:

  • v=469.62m/sv = 469.62 \, \text{m/s},
  • f=262Hzf = 262 \, \text{Hz}:

L=469.622×262L = \frac{469.62}{2 \times 262}

L0.896mL \approx 0.896 \, \text{m}


Part 3: Length of the Closed-Open Tube

The fundamental frequency ff for a pipe closed at one end is given by:

f=vair4Lpipef = \frac{v_{\text{air}}}{4L_{\text{pipe}}}

Where vairv_{\text{air}} is the speed of sound in air. Assuming standard conditions:

vair=343m/sv_{\text{air}} = 343 \, \text{m/s}

Rearranging to find LpipeL_{\text{pipe}}:

Lpipe=vair4fL_{\text{pipe}} = \frac{v_{\text{air}}}{4f}

Substitute:

  • vair=343m/sv_{\text{air}} = 343 \, \text{m/s},
  • f=262Hzf = 262 \, \text{Hz}:

Lpipe=3434×262L_{\text{pipe}} = \frac{343}{4 \times 262}

Lpipe0.327mL_{\text{pipe}} \approx 0.327 \, \text{m}


Summary of Results

  1. Wave Speed on the String: v469.62m/sv \approx 469.62 \, \text{m/s}.
  2. Length of the String: L0.896mL \approx 0.896 \, \text{m}.
  3. Length of the Closed-Open Tube: Lpipe0.327mL_{\text{pipe}} \approx 0.327 \, \text{m}.

Would you like further clarifications or a deeper dive into these concepts?


Relative Questions

  1. What is the relationship between tension and wave speed on a string?
  2. How does the length of a closed-open tube affect its fundamental frequency?
  3. Why does the wave speed depend on the mass per unit length in a string?
  4. What are some real-world factors that might affect the speed of sound in air?
  5. How would the results change if the pipe were open at both ends?

Tip

For a string, increasing tension increases wave speed, while increasing mass per

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Wave mechanics
Fundamental frequency
Harmonics
Speed of sound

Formulas

Wave speed: v = sqrt(T / μ)
Fundamental frequency for string: f = v / 2L
Fundamental frequency for closed-open pipe: f = v_air / 4L

Theorems

Wave equation on a string
Harmonic resonance principles

Suitable Grade Level

Grades 10-12