Waves, Sound and Light: Light Waves

Light Waves: Audio Guided Solution

Problem 13:

Mr. H takes his class to the gymnasium to investigate two point source interference patterns produced by sound waves from two sound sources. The pure-tone output from a frequency generator is split and fed to two audio speakers positioned about 1-meter apart. The sound from the two speakers travels through the gymnasium and interferes constructively and destructively to create a pattern of nodes and antinodes. Mr. H directs the class to stand with one ear facing the speakers and the other ear covered and to walk slowly across the gymnasium, observing positions of relatively soft and loud sounds in alternating fashion. Once initial observations are made, Mr. H asks all the male students to stand at nodal positions and all the female students to stand at antinodal positions. Once done, Mr. H takes a picture of their positions and then makes several measurements of the distances between students and from some selected students to the speakers. Some sample data are shown below. Complete the table, determining the wavelength of the sound waves based on each student’s measurements.

Student Nodal or
Antinodal Line
Distance to
Speaker 1 (m)
Distance to
Speaker 2 (m)
Wavelength (m)
Jeremy 1st Nodal 14.45 13.52  
Bridget 1st Antinodal 21.64 23.42  
Jane 3rd Antinodal 16.22 21.67  
Jose 4th Nodal 25.22 19.10  

Audio Guided Solution

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Habits of an Effective Problem Solver

  • Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
  • Identify the known and unknown quantities and record in an organized manner, often times they can be recorded on the diagram itself. Equate given values to the symbols used to represent the corresponding quantity (e.g., v = 3.00x108 m/s, λ = 554 nm, f = ???).
  • Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
  • Identify the appropriate formula(s) to use.
  • Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.

Read About It!

Get more information on the topic of Light Waves at The Physics Classroom Tutorial.

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