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The model for the Ehrenfest chain consists of 2 boxes containing a total of n balls, where n is any integer greater than or equal to 2. In each turn, a ball is picked at random and moved from whatever box it is in to the other box. Let the state of the Markov process be the number of balls in the first box. (a) Verify that the probability of going from state i to state j is given by the following.

pij={in if i1 and j=i11in if in1 and j=i+11 if i=0 and j=1 or i=n and j=n10 otherwise.p_{i j}=\left\{\begin{array}{ll}\frac{i}{n} & \text { if } i \geq 1 \text { and } j=i-1 \\ 1-\frac{i}{n} & \text { if } i \leq n-1 \text { and } j=i+1 \\ 1 & \text { if } i=0 \text { and } j=1 \text { or } i=n \text { and } j=n-1 \\ 0 & \text { otherwise.}\end{array}\right.

(b) Verify that the transition matrix is given by

 0123n00100011n011n00202n012n0n00000\begin{array}{l} \text{ } & \text{0} & \text{1} & \text{2} & \text{3} & \text{$\cdots$} & \text{n}\\ \\ \text{0} && \text{0} & \text{1} & \text{0} & \text{0} & \text{$\cdots$} & \text{0}\\ \text{1} && \text{$\frac{1}{n}$} & \text{0} & \text{$1-\frac{1}{n}$} & \text{0} & \text{$\cdots$} & \text{0}\\ \text{2} && \text{0} & \text{$\frac{2}{n}$} & \text{0} & \text{$1-\frac{2}{n}$} & \text{$\cdots$} & \text{0}\\ \text{$\vdots$} && \text{$\vdots$} & \text{$\vdots$} & \text{$\vdots$} & \text{$\vdots$} & \text{$\vdots$} & \text{$\vdots$}\\ \text{n} && \text{0} & \text{0} & \text{0} & \text{0} & \text{$\cdots$} & \text{0}\\ \end{array}

(c) Write the transition matrix for the case n=2. (d) Determine whether the transition matrix in part (c) is a regular transition matrix. (e) Determine an equilibrium vector for the matrix in part (c). Explain what the result means.

Question

An energy of about 21 eV is required to excite an electron in a helium atom from the 1s state to the 2s state. The same transition for the He+\mathrm{He}^{+} ion requires about twice as much energy. Explain why this is so.

Solution

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As we know, the expression for the transition energy is given by:

En=22n2(13.6eV)\begin{align*} E_{n}&=\frac{2^2}{n^2} (-13.6 \: \text{eV}) \tag{Where is $n$ the number of states.}\\ \end{align*}

The transition energy for He+\text{He}^ {+} is about twice as He. In a neutral atom, one electron is moving in the field of a nucleus and the field of another electron. The nucleus contains two protons of charge +ze+ze it moves in the field of a net charge.

qnet=+2eeqnet=+e\begin{align*} q_{net}&=+2e-e\\ q_{net}&=+e\\ \end{align*}

The electron in the atom He+\text{He}^{+} moves in the field of zeze. So, the potential energy function for the electron is about double that of one electron in the neutral atom.

For He atom, the transition energy is:

E2E1=21eVE_{2}-E_{1}=21 \: \text{eV}

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