How Was the Equation v=fλ Derived in Wave Physics?

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SUMMARY

The equation v=fλ, which describes the relationship between wave velocity (v), frequency (f), and wavelength (λ), is derived from fundamental principles of wave motion. It is established that velocity is defined as v=Δx/Δt, where Δx represents the wavelength (λ) and Δt corresponds to the wave period (T). By substituting T with 1/f (the reciprocal of frequency), the equation simplifies to v=λf. This derivation highlights the straightforward nature of wave mechanics rather than a complex historical evolution.

PREREQUISITES
  • Understanding of basic wave properties, including wavelength and frequency.
  • Familiarity with the concept of wave velocity.
  • Knowledge of the wave equation c²∇²f = ∂²f/∂t².
  • Basic algebra for manipulating equations.
NEXT STEPS
  • Research the derivation and applications of the wave equation c²∇²f = ∂²f/∂t².
  • Explore the relationship between wave speed, tension, and mass density in waves on a string.
  • Learn about the physical significance of frequency and period in wave phenomena.
  • Investigate different types of waves, such as longitudinal and transverse waves, and their characteristics.
USEFUL FOR

Students and educators in physics, particularly those studying wave mechanics, as well as anyone interested in the mathematical foundations of wave behavior.

Musa Ali
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Hi,

We were recently testing out waves on a string and completing a lab based on it, and I wanted to provide background information on how the equation v=fλ was formulated. I would greatly appreciate it if someone could direct me to a source on it.

Thanks.
 
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Let me first tell you that in general the equation you wrote down isn't called the wave equation. The wave equation looks like ##c^{2}\nabla^{2} f = \frac{\partial^{2} f }{\partial t^{2}}##. Anyway the equation you talk about doesn't really have such a history as you might think - it's very easy to reason. The velocity of something is given by ##v=\frac{\Delta x}{\Delta t}## right? Well let's consider the ##\lambda=\Delta x##, what is the corresponding time? It's just what we define to be the period ##T## of the wave, namely, how much times it takes for one wavelength to pass. And so we have ##v=\frac{\lambda}{T}##. The fraction ##\frac{1}{T}## corresponds to the frequency ##f## and so we arrive at ##v=\lambda f##
 

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