From 05c61c6c96a72fdbcfbe6800519d2dc5b91db013 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Sat, 20 Feb 2021 16:01:15 +0100 Subject: Fix derivatives in "Probability current" --- latex/know/concept/probability-current/source.md | 10 +++++----- static/know/concept/probability-current/index.html | 10 +++++----- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/latex/know/concept/probability-current/source.md b/latex/know/concept/probability-current/source.md index a6780f7..69faf0c 100644 --- a/latex/know/concept/probability-current/source.md +++ b/latex/know/concept/probability-current/source.md @@ -14,8 +14,8 @@ its derivative with respect to time $t$, and when necessary substitute in the other side of the Schrödinger equation to get: $$\begin{aligned} - \pd{P}{t} - &= \int_{V} \psi \pd{\psi^*}{t} + \psi^* \pd{\psi}{t} \dd[3]{\vec{r}} + \pdv{P}{t} + &= \int_{V} \psi \pdv{\psi^*}{t} + \psi^* \pdv{\psi}{t} \dd[3]{\vec{r}} = \frac{i}{\hbar} \int_{V} \psi (\hat{H} \psi^*) - \psi^* (\hat{H} \psi) \dd[3]{\vec{r}} \\ &= \frac{i}{\hbar} \int_{V} \psi \Big( \!-\! \frac{\hbar^2}{2 m} \nabla^2 \psi^* + V(\vec{r}) \psi^* \Big) @@ -51,8 +51,8 @@ Returning to the derivation of $\vec{J}$, we now have the following equation: $$\begin{aligned} - \pd{P}{t} - = \int_{V} \pd{|\psi|^2}{t} \dd[3]{\vec{r}} + \pdv{P}{t} + = \int_{V} \pdv{|\psi|^2}{t} \dd[3]{\vec{r}} = - \int_{V} \nabla \cdot \vec{J} \dd[3]{\vec{r}} \end{aligned}$$ @@ -62,7 +62,7 @@ for $\vec{J}$: $$\begin{aligned} \boxed{ \nabla \cdot \vec{J} - = - \pd{|\psi|^2}{t} + = - \pdv{|\psi|^2}{t} } \end{aligned}$$ diff --git a/static/know/concept/probability-current/index.html b/static/know/concept/probability-current/index.html index d736e49..7b7ac32 100644 --- a/static/know/concept/probability-current/index.html +++ b/static/know/concept/probability-current/index.html @@ -56,8 +56,8 @@ \end{aligned}\]

As the system evolves in time, this probability may change, so we take its derivative with respect to time \(t\), and when necessary substitute in the other side of the Schrödinger equation to get:

\[\begin{aligned} - \pd{P}{t} - &= \int_{V} \psi \pd{\psi^*}{t} + \psi^* \pd{\psi}{t} \dd[3]{\vec{r}} + \pdv{P}{t} + &= \int_{V} \psi \pdv{\psi^*}{t} + \psi^* \pdv{\psi}{t} \dd[3]{\vec{r}} = \frac{i}{\hbar} \int_{V} \psi (\hat{H} \psi^*) - \psi^* (\hat{H} \psi) \dd[3]{\vec{r}} \\ &= \frac{i}{\hbar} \int_{V} \psi \Big( \!-\! \frac{\hbar^2}{2 m} \nabla^2 \psi^* + V(\vec{r}) \psi^* \Big) @@ -83,15 +83,15 @@ \end{aligned}\]

Returning to the derivation of \(\vec{J}\), we now have the following equation:

\[\begin{aligned} - \pd{P}{t} - = \int_{V} \pd{|\psi|^2}{t} \dd[3]{\vec{r}} + \pdv{P}{t} + = \int_{V} \pdv{|\psi|^2}{t} \dd[3]{\vec{r}} = - \int_{V} \nabla \cdot \vec{J} \dd[3]{\vec{r}} \end{aligned}\]

By removing the integrals, we thus arrive at the continuity equation for \(\vec{J}\):

\[\begin{aligned} \boxed{ \nabla \cdot \vec{J} - = - \pd{|\psi|^2}{t} + = - \pdv{|\psi|^2}{t} } \end{aligned}\]

This states that probability is conserved, and is reminiscent of charge conservation in electromagnetism. In other words, the probability at a point can only change by letting it “flow” towards or away from it. Thus \(\vec{J}\) represents the flow of probability, which is analogous to the motion of a particle.

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