3. Let X and P be the position and linear momentum operators of a single particle, respectively. The corresponding representations in one-dimensional position space are X ký = xv(x) dv(x) Ph = -ih- dx where x is position and is a wavefunction. a) Find the commutator X, Consider the case of a particle of mass m in a 1-D box of length L, where the wavefunctions are { Vž sin(k,7), 0< x < L 0, Un(x) = otherwise NT kin n e Z, n > 0 L' b) Show that pn is an eigenfunction of the kinetic energy operator corresponding eigenvalue? What is the 2m c) Find < X >. d) Find < P >. e) Find < P² >.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Problem 3**:

Let \( \hat{X} \) and \( \hat{P} \) be the position and linear momentum operators of a single particle, respectively. The corresponding representations in one-dimensional position space are:

\[
\hat{X} \psi = x \psi(x)
\]

\[
\hat{P} \psi = -i \hbar \frac{d\psi(x)}{dx}
\]

where \( x \) is position and \( \psi \) is a wavefunction.

**(a)** Find the commutator \([ \hat{X}, \hat{P} ]\).

Consider the case of a particle of mass \( m \) in a 1-D box of length \( L \), where the wavefunctions are:

\[
\psi_n(x) = 
\begin{cases} 
\sqrt{\frac{2}{L}} \sin(k_n x), & 0 < x < L \\ 
0, & \text{otherwise} 
\end{cases}
\]

\[
k_n = \frac{n \pi}{L}, \quad n \in \mathbb{Z}, \quad n > 0
\]

**(b)** Show that \( \psi_n \) is an eigenfunction of the kinetic energy operator \( \frac{\hat{P}^2}{2m} \). What is the corresponding eigenvalue?

**(c)** Find \( \langle \hat{X} \rangle \).

**(d)** Find \( \langle \hat{P} \rangle \).

**(e)** Find \( \langle \hat{P}^2 \rangle \).
Transcribed Image Text:**Problem 3**: Let \( \hat{X} \) and \( \hat{P} \) be the position and linear momentum operators of a single particle, respectively. The corresponding representations in one-dimensional position space are: \[ \hat{X} \psi = x \psi(x) \] \[ \hat{P} \psi = -i \hbar \frac{d\psi(x)}{dx} \] where \( x \) is position and \( \psi \) is a wavefunction. **(a)** Find the commutator \([ \hat{X}, \hat{P} ]\). Consider the case of a particle of mass \( m \) in a 1-D box of length \( L \), where the wavefunctions are: \[ \psi_n(x) = \begin{cases} \sqrt{\frac{2}{L}} \sin(k_n x), & 0 < x < L \\ 0, & \text{otherwise} \end{cases} \] \[ k_n = \frac{n \pi}{L}, \quad n \in \mathbb{Z}, \quad n > 0 \] **(b)** Show that \( \psi_n \) is an eigenfunction of the kinetic energy operator \( \frac{\hat{P}^2}{2m} \). What is the corresponding eigenvalue? **(c)** Find \( \langle \hat{X} \rangle \). **(d)** Find \( \langle \hat{P} \rangle \). **(e)** Find \( \langle \hat{P}^2 \rangle \).
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