- #1

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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