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authorPrefetch2021-02-20 16:01:15 +0100
committerPrefetch2021-02-20 16:01:15 +0100
commit05c61c6c96a72fdbcfbe6800519d2dc5b91db013 (patch)
treec880186efeab2c731b5dfe5f73d5b6a086ec8053 /static/know/concept
parentce9aef392998e471d41f88beb54d07e58dbf57d3 (diff)
Fix derivatives in "Probability current"
Diffstat (limited to 'static/know/concept')
-rw-r--r--static/know/concept/probability-current/index.html10
1 files changed, 5 insertions, 5 deletions
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}\]</span></p>
<p>As the system evolves in time, this probability may change, so we take its derivative with respect to time <span class="math inline">\(t\)</span>, and when necessary substitute in the other side of the Schrödinger equation to get:</p>
<p><span class="math display">\[\begin{aligned}
- \pd{P}{t}
- &amp;= \int_{V} \psi \pd{\psi^*}{t} + \psi^* \pd{\psi}{t} \dd[3]{\vec{r}}
+ \pdv{P}{t}
+ &amp;= \int_{V} \psi \pdv{\psi^*}{t} + \psi^* \pdv{\psi}{t} \dd[3]{\vec{r}}
= \frac{i}{\hbar} \int_{V} \psi (\hat{H} \psi^*) - \psi^* (\hat{H} \psi) \dd[3]{\vec{r}}
\\
&amp;= \frac{i}{\hbar} \int_{V} \psi \Big( \!-\! \frac{\hbar^2}{2 m} \nabla^2 \psi^* + V(\vec{r}) \psi^* \Big)
@@ -83,15 +83,15 @@
\end{aligned}\]</span></p>
<p>Returning to the derivation of <span class="math inline">\(\vec{J}\)</span>, we now have the following equation:</p>
<p><span class="math display">\[\begin{aligned}
- \pd{P}{t}
- = \int_{V} \pd{|\psi|^2}{t} \dd[3]{\vec{r}}
+ \pdv{P}{t}
+ = \int_{V} \pdv{|\psi|^2}{t} \dd[3]{\vec{r}}
= - \int_{V} \nabla \cdot \vec{J} \dd[3]{\vec{r}}
\end{aligned}\]</span></p>
<p>By removing the integrals, we thus arrive at the <em>continuity equation</em> for <span class="math inline">\(\vec{J}\)</span>:</p>
<p><span class="math display">\[\begin{aligned}
\boxed{
\nabla \cdot \vec{J}
- = - \pd{|\psi|^2}{t}
+ = - \pdv{|\psi|^2}{t}
}
\end{aligned}\]</span></p>
<p>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 <span class="math inline">\(\vec{J}\)</span> represents the flow of probability, which is analogous to the motion of a particle.</p>