Expansion of the wave equation for a stationary wave

FR5LV6fQKMmWjwOZ5LWgDQIn summary, the conversation discusses the expansion of a generic state represented by a wave function in terms of eigenstates with defined angular momentum. It is shown that the coefficients for a plane wave traveling along the z direction with momentum ##p = \hbar k## are non-zero only if ##k' = k## and ##m = 0##. This can be solved by using dimensionless variables and a power series ansatz, but there may be a simpler approach.
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John Greger
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Homework Statement


A generic state represented by the wave function ##\psi (\vec(x)## can be expanded in the eigenstates with defined angular momentum. Write such an expansion for a plane wave traveling along the z direction with momentum ##p = \hbar k## in terms of unknown coefficients ##c ( k ′ )_ {l m}## . Show that ##c ( k )_{ l m} are non-zero only if k' = k and m = 0

Homework Equations

The Attempt at a Solution



I don't know where to start. I could of course go the long way, introducing dimensionless variables, do a power series ansatz and solve de DE with frobinious trick. But it seems the answer will be way easier than that if you just know how to approach it.
 
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Related to Expansion of the wave equation for a stationary wave

1. What is the wave equation for a stationary wave?

The wave equation for a stationary wave is a mathematical representation of the behavior of a wave that does not propagate or move in space. It is described by the equation y(x,t) = A*sin(kx)*cos(ωt), where A is the amplitude, k is the wave number, x is the position, ω is the angular frequency, and t is the time.

2. How is the wave equation for a stationary wave expanded?

The wave equation for a stationary wave can be expanded using trigonometric identities, such as the double angle and half angle formulas, to simplify and further analyze the behavior of the wave. It can also be expanded using Fourier series to represent the wave as a sum of sine and cosine functions with different frequencies and amplitudes.

3. What is the significance of the expansion of the wave equation for a stationary wave?

The expansion of the wave equation for a stationary wave allows for a deeper understanding of the properties and behavior of the wave. It also allows for the analysis of different factors, such as boundary conditions and initial conditions, that can affect the wave's behavior. This expansion is essential in many fields, including optics, acoustics, and quantum mechanics.

4. Can the expansion of the wave equation for a stationary wave be applied to real-life situations?

Yes, the expansion of the wave equation for a stationary wave can be applied to real-life situations. For example, it can be used to analyze standing waves in musical instruments, electromagnetic waves in antennas, and even the behavior of particles in quantum mechanics. Its applications are widespread and essential in understanding many natural phenomena.

5. Are there any limitations to the expansion of the wave equation for a stationary wave?

While the expansion of the wave equation for a stationary wave is a powerful tool, it does have some limitations. For instance, it assumes that the medium in which the wave is propagating is uniform and isotropic, which may not always be the case in real-life situations. Additionally, it only applies to linear waves, and more complex phenomena may require different equations or methods for analysis.

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