5.2 Waves and Wavelengths

5.2 Waves and Wavelengths

Learning Objectives

  • By the end of this section, students will be able to:

    • Describe important physical features of wave forms.

    • Show how physical properties of light waves are associated with perceptual experience.

    • Show how physical properties of sound waves are associated with perceptual experience.

General Overview

  • Visual and auditory stimuli both occur in the form of waves.

  • Despite differences in composition, wave forms share similar characteristics that are crucial for visual and auditory perceptions.

Physical Properties of Waves

Amplitude and Wavelength

  • Two essential physical characteristics of a wave:

    • Amplitude:

    • Definition: The distance from the center line to the top point of the crest or the bottom point of the trough.

    • Wavelength:

    • Definition: The length of a wave measured from one peak to the next.

    • Measurement of wavelength is shown in Figure 5.4; it is related to the characteristics of wave height.

Relationship Between Wavelength and Frequency

  • Wavelength is directly related to the frequency of a given wave form.

  • Frequency:

    • Definition: Refers to the number of waves that pass a given point in a given time period, typically expressed in hertz (Hz), or cycles per second.

  • The relationship:

    • Longer wavelengths correspond to lower frequencies.

    • Shorter wavelengths correspond to higher frequencies.

Light Waves

  • Visible Spectrum:

    • Definition: The portion of the larger electromagnetic spectrum that humans can perceive.

    • Range: Wavelengths from 380 to 740 nm (nanometers), where 1 nanometer equals one billionth of a meter.

  • Electromagnetic Spectrum:

    • Encompasses all electromagnetic radiation, including:

    • Gamma rays

    • X-rays

    • Ultraviolet light

    • Visible light

    • Infrared light

    • Microwaves

    • Radio waves

  • Other Species' Perception:

    • Honeybees detect ultraviolet light (Wakakuwa, Stavenga, & Arikawa, 2007).

    • Some snakes can sense infrared radiation (Chen et al., 2012; Hartline et al., 1978).

  • Color Perception Related to Wavelength:

    • Our perception of color correlates with the wavelength of light:

    • Longer wavelengths = red

    • Intermediate wavelengths = green

    • Shorter wavelengths = blue and violet

    • Mnemonic for color order in the visible spectrum: ROYGBIV (red, orange, yellow, green, blue, indigo, violet).

  • Brightness and Amplitude:

    • The amplitude of light waves is associated with brightness or intensity.

    • Larger amplitudes appear brighter.

Sound Waves

  • Similar to light waves, the physical properties of sound waves relate to various aspects of sound perception.

  • Frequency and Pitch:

    • Frequency of a sound wave correlates with perceived pitch:

    • High-frequency sound waves = high-pitched sounds.

    • Low-frequency sound waves = low-pitched sounds.

  • Audible Range of Sound Frequencies:

    • Human audible range: Between 20 and 20000 Hz.

    • Greatest sensitivity: Frequencies in the middle of this range.

  • Variation Among Species:

    • Chickens: 125 to 2000 Hz.

    • Mice: 1000 to 91000 Hz.

    • Beluga whales: 1000 to 123000 Hz.

    • Dogs: 70 to 45000 Hz.

    • Cats: 45 to 64000 Hz (Strain, 2003).

  • Loudness and Amplitude:

    • Loudness is closely related to the amplitude of sound waves.

    • Higher amplitudes produce louder sounds.

  • Measurement of Loudness:

    • Measured in decibels (dB), a logarithmic unit of sound intensity.

    • Example sounds with corresponding dB levels:

    • Typical conversation: 60 dB.

    • Rock concert: 120 dB.

  • Hearing Damage Risks:

    • Sounds between 80 dB and 130 dB can cause hearing damage:

    • Food processor, power lawnmower, heavy truck (25 feet away), subway train (20 feet away), live rock music, jackhammer.

    • Threshold for pain: about 130 dB (e.g., jet plane taking off, revolver firing at close range) (Dunkle, 1982).

Interaction of Frequency and Amplitude in Sound

  • While amplitude generally correlates with loudness, there is an interaction between frequency and amplitude in sound perception:

    • A 10 Hz sound wave is inaudible regardless of amplitude.

    • A 1000 Hz sound wave's perceived loudness significantly increases with rising amplitude.

  • Timbre:

    • Definition: The purity of a sound, influenced by the complex interplay of frequency, amplitude, and timing of sound waves.

    • Different musical instruments can produce the same note with the same loudness but will still sound distinctly different due to differences in timbre.

Links and References

  • A brief video demonstrating frequency and amplitude interaction in loudness is suggested for further understanding.