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 = xb(x) dy(x) Puy = -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 sin(knx), 0 0 L' b) Show that n is an eigenfunction of the kinetic energy operator corresponding eigenvalue? What is the 2m c) Find < X >.

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**Quantum Mechanics Problem Set**

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

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

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

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 wave functions are

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

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

**b) Show that \( \psi_n \) is an eigenfunction of the kinetic energy operator \( \dfrac{\hat{P}^2}{2m} \). 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:**Quantum Mechanics Problem Set** 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 \[ \hat{X} \psi = x \psi(x) \] \[ \hat{P} \psi = -i \hbar \dfrac{d \psi(x)}{dx} \] 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 wave functions are \[ \psi_n(x) = \begin{cases} \sqrt{\dfrac{2}{L}} \sin(k_n x), & 0 < x < L \\ 0, & \text{otherwise} \end{cases} \] \[ k_n = \dfrac{n \pi}{L}, \, n \in \mathbb{Z}, \, n > 0 \] **b) Show that \( \psi_n \) is an eigenfunction of the kinetic energy operator \( \dfrac{\hat{P}^2}{2m} \). 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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