Derive the Schrodinger’s Time Dependent differential equation for matter waves
Q.3 (b) Derive the Schrodinger’s Time Dependent differential equation for matter waves
Q.3 (b) Derive the Schrodinger’s Time Dependent differential equation for matter waves
Best answer
A free particle moving along x is described by the wave function
\[ \psi(x,t)=A\,e^{-i(Et-px)/\hbar} \]
using \(E=\hbar\omega\) and \(p=\hbar k\).
Step 1 (time derivative): \(\dfrac{\partial\psi}{\partial t}=-\dfrac{iE}{\hbar}\psi\Rightarrow E\psi=i\hbar\dfrac{\partial\psi}{\partial t}\) ... (1)
Step 2 (space derivative): \(\dfrac{\partial\psi}{\partial x}=\dfrac{ip}{\hbar}\psi\), so \(\dfrac{\partial^2\psi}{\partial x^2}=-\dfrac{p^2}{\hbar^2}\psi\Rightarrow p^2\psi=-\hbar^2\dfrac{\partial^2\psi}{\partial x^2}\) ... (2)
Step 3 (energy): Total energy \(E=\dfrac{p^2}{2m}+V\). Multiplying by ψ: \(E\psi=\dfrac{p^2}{2m}\psi+V\psi\) ... (3)
Substituting (1) and (2) into (3):
\[ \boxed{i\hbar\frac{\partial\psi}{\partial t}=-\frac{\hbar^2}{2m}\frac{\partial^2\psi}{\partial x^2}+V\psi} \]
This is the one-dimensional time-dependent Schrödinger equation. In three dimensions: \(i\hbar\dfrac{\partial\psi}{\partial t}=\Big(-\dfrac{\hbar^2}{2m}\nabla^2+V\Big)\psi=\hat H\psi\), where \(\hat H\) is the Hamiltonian operator. The operator correspondences are \(E\to i\hbar\,\partial/\partial t\) and \(p\to-i\hbar\,\partial/\partial x\).
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