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🔋college physics i – introduction review

V = fλ

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The equation v = fλ, known as the wave speed equation, describes the relationship between the speed (v) of a wave, its frequency (f), and its wavelength (λ). This fundamental equation is central to the understanding of wave phenomena, including the Doppler effect and sonic booms.

5 Must Know Facts For Your Next Test

  1. The wave speed equation, v = fλ, demonstrates that the speed of a wave is directly proportional to its frequency and inversely proportional to its wavelength.
  2. This equation is fundamental to understanding the Doppler effect, which describes the change in the observed frequency of a wave due to the relative motion between the source and the observer.
  3. The wave speed equation is also crucial in analyzing sonic booms, which occur when an object moves faster than the speed of sound, creating a shock wave that travels at the speed of sound.
  4. The frequency and wavelength of a wave are inversely related, meaning that as the frequency increases, the wavelength decreases, and vice versa.
  5. The wave speed equation can be used to predict the behavior of various types of waves, including sound waves, electromagnetic waves, and water waves.

Review Questions

  • Explain how the wave speed equation, v = fλ, relates to the Doppler effect.
    • The Doppler effect is the change in the observed frequency of a wave due to the relative motion between the source and the observer. The wave speed equation, v = fλ, is central to understanding the Doppler effect because it demonstrates that the speed of a wave is directly proportional to its frequency. When a source of waves is moving relative to an observer, the observed frequency of the waves will be different from the frequency emitted by the source, as the wave speed remains constant. This change in observed frequency is the Doppler effect, and the wave speed equation provides the mathematical relationship that describes this phenomenon.
  • Describe how the wave speed equation can be used to analyze sonic booms.
    • Sonic booms occur when an object, such as an aircraft, moves faster than the speed of sound. The wave speed equation, v = fλ, is crucial in understanding this phenomenon. When an object moves faster than the speed of sound, it creates a shock wave that travels at the speed of sound. The wavelength of this shock wave is determined by the speed of the object and the speed of sound, as described by the wave speed equation. The shorter the wavelength of the shock wave, the more intense the sonic boom experienced by observers on the ground. By applying the wave speed equation, scientists and engineers can predict the characteristics of sonic booms, such as their intensity and the area affected, based on the speed and size of the object creating the disturbance.
  • Analyze how the inverse relationship between frequency and wavelength, as described by the wave speed equation, affects the propagation of waves.
    • The wave speed equation, v = fλ, demonstrates the inverse relationship between the frequency and wavelength of a wave. This relationship has significant implications for the propagation of waves. As the frequency of a wave increases, its wavelength decreases, and vice versa. This means that waves with higher frequencies can transmit more information or energy over a given distance, as they have shorter wavelengths and can interact with smaller-scale features in the medium. Conversely, waves with lower frequencies have longer wavelengths and can propagate through larger obstacles or over longer distances without being as easily scattered or absorbed. Understanding this inverse relationship, as described by the wave speed equation, is crucial for designing and optimizing wave-based technologies, such as communication systems, radar, and medical imaging devices.