diff --git a/ueb8.tex b/ueb8.tex new file mode 100644 index 0000000..80cf63a --- /dev/null +++ b/ueb8.tex @@ -0,0 +1,143 @@ +\chapter{Quantenmechanik I - Übungsblatt 8} +\section{Aufgabe 20: Dirac-Kamm} +\subsection*{a)} +Für $0 < x < a$ und $V(x) = 0$: +$-\frac{\hbar^2}{2 m} \Phi'(x) = E \Phi(x)$ +$\Rightarrow$ +$\Phi(x) = A \cdot \sinb{k x} + B \cdot \cosb{k x}$ mit $k = \sqrt{\frac{2 m E}{\hbar}}$ + +Für $0 > x > -a$: +$\Phi(x) = e^{-\i K a} \cdot \sbk{ A \sinb{k a} + B \cosb{k a}}$ +$k A - e^{-\i K a} \sbk{A \cosb{k a} + B \sinb{k a}} = -\frac{2 n \alpha B}{\hbar^2}$ +$\mu \inlinematrix{A \\ B} = \inlinematrix{0 \\ 0}$ +$\inlinematrix{A \\ B} = \frac{1}{\mu} \inlinematrix{0 \\ 0}$ +$\Rightarrow$ +$A=0$ und $B=0$ +$\Rightarrow$ +$\detb{\mu} = 0$ da sonst $A=B=0$. +$\cosb{K a} = \cosb{k a} - \frac{n \alpha}{\hbar k} \sinhb{a}$ +$\cosb{Z} = \cosb{Z} - \beta \frac{\sinb{Z}}{Z}$ +\subsection*{b)} +%grafik plotten und hier einfügen +\subsection*{c)} + +\begin{align} + \cosb{K a} &= \cosb{k a} - B \frac{\sinb{k a}}{k a} &\left| k = \i k \right. \\ + \cosb{K a} &= \cosb{k a} - B \frac{\sinhb{k a}}{k a} +\end{align} + + +\section{Aufgabe 21: Lineares Potential} +\subsection*{a)} +$V(x) = m g x$ +Die Schrödingergleichung lautet: +\equationblock{\sbk{-\frac{\hbar^2}{2 m} \diffPs{x}^2 + V(x + a)} \psi(x + a) = E \psi(x + a)} +$\Rightarrow$ +\equationblock{\sbk{-\frac{\hbar^2}{2 m} \diffPs{x}^2 + V(x)} \psi(x + a) = \sbk{E - V(a)} \psi(x + a)} +$E = m g a$ +\subsection*{b)} +\begin{math} + \inlinematrix{kg \\ m \\ s} + m = \sqbk{kg} \inlinematrix{1 \\ 0 \\ 0} + g = \ssbk{\frac{m}{s^2}} = \inlinematrix{0 \\ 1 \\ -2} + \hbar = \ssbk{Js} = \ssbk{\frac{kg m^2}{s}} = \inlinematrix{1 \\ 2 \\ -1} + T_0 = \inlinematrix{0 \\ 0 \\ 1} \inlinematrix{1 & 0 & 1 \\ 0 & 1 & 2 \\ 0 & -2 & 1} \inlinematrix{0 \\ 0 \\ 1} + T_0 = \sqrt[3]{\frac{\hbar}{m g ^2}} + L_0 = \sqrt[3]{\frac{\hbar^2}{m^2 g}} + E_0 = \sqrt[3]{m \hbar^2 g^2} + P_0 = \sqrt[3]{m^2 \hbar g} +\end{math} +% +\begin{align} + \sbk{-\frac{\hbar^2}{2 m} J^2_{L_0y} + m g L_0 y} \frac{\psi(y)}{\sqrt{L_0}} &= \epsilon E_0 \frac{\psi(y)}{\sqrt{L_0}} \\ + \sbk{-\frac{1}{2} E_0 J_y^2 + E_0 y} \psi(y) &= \epsilon E_0 \psi(y) \\ + \sbk{-\frac{1}{2} J_y^2 + y} \psi(y) &= \epsilon \psi(y) \\ + \psi(p) &= \frac{1}{\sqrt{p}} \Phi \\ + \frac{1}{2} k^2 \Phi(k) + \i \diffPfrac{\Phi(k)}{k} &= \epsilon \Phi(k) \\ + \partial y &\Rightarrow \i k \\ + y &\Rightarrow \i \partial k \\ + \Phi(p) &= \intgrinf{\frac{1}{2 \pi \hbar} e^{-\frac{\i}{\hbar} p x} \Phi(x)}{x} \\ + \frac{\Phi(k)}{\sqrt{p_0}} &= \intgrinf{\frac{1}{L_0 2 \pi \hbar} e^{\frac{\i}{\hbar} y L_0 k p_0} \Phi(y)}{y L_0} \\ + \Phi(k) &= \sqrt{\frac{p_0 L_0}{2 \pi \hbar}} \intgrinf{e^{-\frac{\i}{\hbar} L_0 I_0 k y} \Phi(y)}{y} \\ + &= \frac{1}{\sqrt{2 \pi}} \intgrinf{e^{\i k y} \Phi(y)}{y} +\end{align} +% +\subsection*{c)} +$\sbk{\frac{1}{2} k^2 + \i \diffPs{k}} \Phi_0(k) = 0$ +Trennung der Variable führt auf: +$\Phi_0(k) = c \cdot e^{\frac{\i}{6} k^3}$ +Fourriertansformation: +\begin{align} + \psi_0(y) &= \frac{1}{\sqrt{2 \pi}} \intgrinf{e^{\i k y} \Phi(k)}{k} \\ + &= \frac{c}{\sqrt{2 \pi}} \intgrinf{\sbk{\cosb{\frac{1}{6} k^3 + k y} + \i \sinb{\frac{1}{6} k^3 + k y}}}{k} \\ +\end{align} +da $\intgrinf{\sinb{x}}{x} = 0$ +\begin{align} + \psi_0(y) &= \frac{c}{\sqrt{2 \pi}} \intgrinf{\cosb{\frac{1}{6} k^3 + k y}}{k} +\end{align} +mit $\frac{1}{6} k^3 = \frac{1}{3} \tilde{k}^3$ +\begin{align} + \psi_0(y) &= c \frac{\sqrt[6]{2^5}}{\sqrt{\pi}} \intgrinf{\cosb{\frac{1}{3} \tilde{k} + \sqrt[3]{2} \tilde{k} y}}{\tilde{k}} \\ + &= 2^6 \sqrt{\pi} \airyb{\sqrt[3]{2} y} \\ + &= \psi_0(y) +\end{align} +aus Teil a): +$\psi_\epsilon(x) = \psi_0(x - \frac{E}{m g})$ +folgt somit: +\begin{align} + \psi_\epsilon(y) &= \sqrt{L_0} \psi_0(L_o y - \epsilon L_0) \\ + &= \psi_0(y - \epsilon) \\ + &= 2^\frac{5}{6} \sqrt{\pi} c \airyb{\sqrt[3]{2} \sbk{y - \epsilon}} \\ + \Phi_\epsilon(t) &= e^{-\i k \epsilon} \Phi_0{k} \\ + &= c \cdot e^{\i \sbk{\frac{k^3}{6} - \epsilon k}} +\end{align} + +\subsection*{d)} +\begin{align} + \intgrinf{\Phi_\epsilon^\ast(k) \Phi_\epsilon(k)}{k} &= \intgrinf{\abs{A}^2 e^{\i k \sbk{\epsilon' - \epsilon}}}{k} \\ + &= \intgrinf{\frac{1}{\sqrt{2 \pi}} e^{\i k \sbk{\epsilon' - \epsilon}}}{k} \\ + A &= \frac{1}{\sqrt{2 \pi}} \\ + \intgrinf{\Phi_\epsilon^\ast(k') \Phi_\epsilon(k)}{\epsilon} &= + \frac{1}{2 \pi} \intgrinf{e^{\i \sbk{k' - k} \epsilon} e^{-\frac{1}{6} \sbk{k'^3 - k^3}}}{\epsilon} \\ + &= e^{-\frac{1}{6} \sbk{k'^3 - k^3}} \intgrinf{\frac{e^{\i \epsilon \sbk{k' - k}}}{2 \pi}}{\epsilon} \\ + &= \delta\sbk{k' - k} \\ + \psi_\epsilon(x) &= \frac{\sqrt[3]{2 m \sqrt{g}}}{\hbar} \airyb{\sqrt[3]{\frac{2 g m^2}{\hbar^2}} \sbk{x - \frac{E}{m g}}} +\end{align} + +\subsection*{e)} +$\sbk{-\frac{1}{2} \diffPs{y}^2 + y} \Psi(y) = 0$ +\subsubsection*{i)} + $e^{f(y)}$ + $f''(y) + \sbk{f'(y)}^2 = 2 y$ +\subsubsection*{ii)} + $g'(y) + g^2(y) = 2 y$ + $g(y) = c_1 y^{\lambda_1}$ + Potenzreihenansatz: + $c_1 \lambda_1 y^{\lambda_1 -1} + c_1^2 y^{2 \lambda_1} = 2 y$ + Asymptotik muss gleich sein: + \begin{align} + 2 \lambda_1 &= 1 \Rightarrow \lambda_1 = \frac{1}{2}\\ + c_1^2 &= 2 \Rightarrow c_1^2 = \pm \sqrt{2} \\ + g_1(y) &= \pm \sqrt{2 y} + \end{align} +\subsubsection*{iii)} +$g_1(y) = g_0(y) + c_2 y^{\lambda_2} = \pm \sqrt{2 y} + c_2 y^{\lambda_2}$ +$\pm \frac{1}{\sqrt{2}} y^{-\frac{1}{2}} + \lambda_2 c_2 y^{\lambda_2 -1} \pm 2 \sqrt{2} c_2 y^{\frac{1}{2} + \lambda_2} + c_2^2 y^{2 \lambda_2} = 0$ +$\pm \frac{1}{\sqrt{2}} y^{-\frac{1}{2}} \sbk{1 \pm \sqrt{2} \lambda_2 c_2 y^{\lambda_2 - \frac{1}{2}} + 4 c_2 y^{\lambda_2 -1} \pm \sqrt{2 c_2^2 y^{2 \lambda + \frac{1}{2}}}} = 0$ +$\lambda_2 = -1$ +$c_2 = -\frac{1}{4}$ +$g(y) = \pm \sqrt{2 y} - \frac{1}{4 y}$ +$f(y) = - \frac{2 \sqrt{2}}{3} y^{\frac{3}{2}} - \frac{\lnb{y}}{4} + c$ +$\Rightarrow$ +$\psi_0(y) 2 e^{-\frac{2 \sqrt{2}}{3}} y^{\frac{3}{2}} \frac{1}{\abs{y}^4}$ +\subsubsection*{iv)} +$V(x) = \begin{cases} + m g x & x > 0 \\ \infty & x \leq 0 + \end{cases}$ +$\psi(0) \deq 0$ +$\psi_E(x) = \airyb{\frac{\sqrt[3]{2 g m^2}}{\hbar^2} \cdot \sbk{-\frac{E}{m g}}}$ +$-\frac{E}{m g} \frac{\sqrt[3]{2 g m^2}}{\hbar^2} \approx -2,3$ +$\Rightarrow$ +$E \approx 1,41 peV$ + +\subsection*{f)} \ No newline at end of file