Characteristics of Periodic Waves
Frequency, cycles, pitch, and how repeating waves are measured
What form of energy travels through the auditory nerve?
How the Ear Works
Video Instruction
showmethephysics.com
Review: Frequency, Amplitude & Wavelength
Sound Waves on Film
ERPI Classroom Films · Encyclopedia Britannica · Prelinger Archives · Public domain
School blocks YouTube? Use the onsite MP4.
What is this speaker component called? What kind of waves does it produce—high or low frequency?
Woofer: it outputs low-frequency waves.
II. Characteristics of Periodic Waves
Frequency is determined by the source of a wave—not by the medium.
Cycles
How many cycles are between the dots?
3 cycles
Frequency Example
10 cycles pass a fixed point in 5 seconds. What is the frequency?
Longitudinal or Transverse?
Periodic-Wave Practice
A wave generator operates for 4 seconds and produces the wave train below.
How many waves are drawn between A and B?
What is the frequency of the wave train?
8 cycles
f = 8 cycles ÷ 4 s = 2 Hz
2 cycles pass a fixed point in 10 seconds. What is the frequency?
What Frequency Means
For sound, frequency determines pitch.
For light, frequency determines color.
The Human Hearing Range
20 Hz–20,000 Hz
Dogs can hear higher-pitched sounds than humans. Your own high-frequency hearing range also changes with age—how old do your ears sound?
Enrichment: How Sound Works
Sound of a Bell in a Vacuum
Enrichment: A Pendulum That Recorded Earthquakes
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. The frequency of a wave is
2. 10 cycles pass a fixed point in 5 seconds. What is the frequency?
3. 2 cycles pass a fixed point in 10 seconds. What is the frequency?
4. The frequency of a wave is determined by
5. A singer moves from a low note to a high note. Which property of the sound wave increased?
The Range of Human Hearing
A healthy young person can hear sounds with frequencies from about 20 Hz to 20,000 Hz. The speed of sound in air at room temperature is about 340 m/s.
What is the wavelength of the lowest-pitched sound a person can hear?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A second sound has a higher pitch than a 440-Hz tone. Both travel through the same room air. Place a check mark in three boxes to indicate how the higher-pitched sound compares with the 440-Hz tone.
C2. A tuning fork vibrates at 440 Hz. What is its period?
C3. Substitute numerical values into a mathematical representation that can be used to determine the wavelength of the highest-pitched sound a young person can hear. Then calculate the wavelength.
C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C5. Dogs can hear up to about 45,000 Hz. Compared with a 20,000-Hz sound, what is true of a 45,000-Hz sound in the same air?
C6. Musicians wear special “high-fidelity” earplugs designed to protect their hearing without making music sound different. Identify which property of the sound wave the earplugs should reduce and which property should stay the same, and explain your answer.
