University Physics IV · unit UPIV-06
The Schrödinger Equation
Connect the ideas, make your working visible, and test the result. Use the hints when you need a starting point; open the full solution after your attempt.
Extra challenging questions
A selection from this pathway. Open a topic below for its complete practice and challenge set.
Building the Schrödinger equation: infer an input with uncertainty
The time-dependent Schrödinger equation is the postulated law of motion for a quantum state: it fixes the rate of change of ψ in time, through a factor of i, from the curvature of ψ in space plus the potential energy at that point. Use the supplied topic model Y_out = exp(-5.7884*q^2*s*cosd(th)), where Y_out is AMPLITUDE |ψ|, 1 AT t = 0 (dimensionless). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793; exp(x) means eˣ; sind/cosd/tand use degrees. th is Phase θ of the coefficient C, measured in °. Keep q (Wavenumber k) = 1 10^10 m^-1; s (Elapsed time t) = 0.2 fs fixed. For this exercise use only 9.5625 ° ≤ th ≤ 80.4375 ° on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 0.49658895, with a bounded reading uncertainty ±0.026592. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown th by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.0070875 °, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.
AMPLITUDE |ψ|, 1 AT t = 0 against th
Predictions from the supplied Building the Schrödinger equation model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): AMPLITUDE |ψ|, 1 AT t = 0
Horizontal axis (x): th: Phase θ of the coefficient C / °
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| th: Phase θ of the coefficient C / ° | AMPLITUDE |ψ|, 1 AT t = 0 |
|---|---|
| 9.5625 | 0.3193096337184467 |
| 27.28125 | 0.35739698859939883 |
| 45 | 0.4410472005910194 |
| 62.71875 | 0.5882326563568182 |
| 80.4375 | 0.8250446999053394 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
The model's endpoint predictions bracket the reading. Solve Y_out(th) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.
Reveal the worked solution
- Endpoint predictions are Y_out(9.5625) = 0.31931 and Y_out(80.4375) = 0.825045. The target lies between them. On the selected branch the response is strictly increasing.
- Endpoint interpolation gives th_line = 9.5625 + (0.496589 − 0.31931)(80.4375 − 9.5625)/(0.825045 − 0.31931) = 34.4069 °. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
- Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives th = 52.7962 °; substituting back gives Y_out = 0.49658895.
- The interpolation error in the input is |th_line − th| = 18.3894 °. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = 0.46999695 and 0.52318095. Sort the roots even if the response decreases: 49.293 ° ≤ th ≤ 55.9724 °.
- The lower and upper input deviations are 3.50329 ° and 3.1762 °. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.
Answer th ≈ 52.7962 °; compatible interval [49.293, 55.9724] °. Endpoint interpolation gives 34.4069 °.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.
Normalisation and the probability current: infer an input with uncertainty
A wavefunction is admissible when it is single-valued, continuous, and square-integrable, and normalising it means dividing by √(∫|ψ|²dx) so that the probability of finding the particle somewhere is exactly one. Use the supplied topic model Y_out = pi/max(k,0.01), where Y_out is FRINGE SPACING π / k (nm). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793; max(a,b) selects the larger value. k is Wavenumber k, measured in nm⁻¹. Keep r (Reflected amplitude r = |B|/|A|) = 0.6 fixed. For this exercise use only 2.6375 nm⁻¹ ≤ k ≤ 7.3625 nm⁻¹ on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 0.56915488 nm, with a bounded reading uncertainty ±0.021368 nm. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown k by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.0004725 nm⁻¹, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.
FRINGE SPACING π / k against k
Predictions from the supplied Normalisation and the probability current model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): FRINGE SPACING π / k / nm
Horizontal axis (x): k: Wavenumber k / nm⁻¹
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| k: Wavenumber k / nm⁻¹ | FRINGE SPACING π / k / nm |
|---|---|
| 2.6375 | 1.1911251767165092 |
| 3.81875 | 0.8226756539678672 |
| 5 | 0.6283185307179586 |
| 6.18125 | 0.5082455253532526 |
| 7.3625 | 0.42670188843324863 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
The model's endpoint predictions bracket the reading. Solve Y_out(k) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.
Reveal the worked solution
- Endpoint predictions are Y_out(2.6375) = 1.19113 nm and Y_out(7.3625) = 0.426702 nm. The target lies between them. On the selected branch the response is strictly decreasing.
- Endpoint interpolation gives k_line = 2.6375 + (0.569155 − 1.19113)(7.3625 − 2.6375)/(0.426702 − 1.19113) = 6.48198 nm⁻¹. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
- Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives k = 5.51975 nm⁻¹; substituting back gives Y_out = 0.56915488 nm.
- The interpolation error in the input is |k_line − k| = 0.962229 nm⁻¹. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = 0.54778688 nm and 0.59052288 nm. Sort the roots even if the response decreases: 5.32002 nm⁻¹ ≤ k ≤ 5.73506 nm⁻¹.
- The lower and upper input deviations are 0.199731 nm⁻¹ and 0.215314 nm⁻¹. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.
Answer k ≈ 5.51975 nm⁻¹; compatible interval [5.32002, 5.73506] nm⁻¹. Endpoint interpolation gives 6.48198 nm⁻¹.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.
Separation of variables and the time-independent equation: infer an input with uncertainty
Separation of variables writes a solution as a function of position alone multiplied by a function of time alone, which reduces the time-dependent Schrödinger equation to the eigenvalue equation Ĥψ = Eψ — but only when the potential has no explicit time dependence. Use the supplied topic model Y_out = cosd(th), where Y_out is REAL PART Re φ (dimensionless). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793; sind/cosd/tand use degrees. th is Phase θ = Eₙt/ħ, measured in °. Keep n (Level n in ψₙ) = 2 fixed. For this exercise use only 189.45 ° ≤ th ≤ 321.75 ° on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 0.0026703506, with a bounded reading uncertainty ±0.1174. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown th by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.01323 °, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.
REAL PART Re φ against th
Predictions from the supplied Separation of variables and the time-independent equation model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): REAL PART Re φ
Horizontal axis (x): th: Phase θ = Eₙt/ħ / °
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| th: Phase θ = Eₙt/ħ / ° | REAL PART Re φ |
|---|---|
| 189.45 | -0.9864292571764955 |
| 222.52499999999998 | -0.7369824847979511 |
| 255.6 | -0.2486898871648553 |
| 288.675 | 0.32019966162731217 |
| 321.75 | 0.7853169308807446 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
The model's endpoint predictions bracket the reading. Solve Y_out(th) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.
Reveal the worked solution
- Endpoint predictions are Y_out(189.45) = -0.986429 and Y_out(321.75) = 0.785317. The target lies between them. On the selected branch the response is strictly increasing.
- Endpoint interpolation gives th_line = 189.45 + (0.00267035 − -0.986429)(321.75 − 189.45)/(0.785317 − -0.986429) = 263.308 °. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
- Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives th = 270.153 °; substituting back gives Y_out = 0.0026703506.
- The interpolation error in the input is |th_line − th| = 6.84486 °. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = -0.11472965 and 0.12007035. Sort the roots even if the response decreases: 263.412 ° ≤ th ≤ 276.896 °.
- The lower and upper input deviations are 6.74103 ° and 6.74316 °. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.
Answer th ≈ 270.153 °; compatible interval [263.412, 276.896] °. Endpoint interpolation gives 263.308 °.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.
Stationary states and superpositions: infer an input with uncertainty
A stationary state is a single energy eigenfunction carrying the phase e^(−iEt/ħ); its probability density and all its expectation values are frozen, so only a superposition of different energies can make anything move. Use the supplied topic model Y_out = 0.5*(0.5+2*sqrt(p*(1-p))*cos(2*pi*t*(n^2-1)/2.7496)*((cos(pi*(n-1))-1)/(pi*(n-1))^2-(cos(pi*(n+1))-1)/(pi*(n+1))^2)), where Y_out is MEAN POSITION ⟨x⟩ (nm). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793; sqrt(x) means √x; unmarked trigonometric functions use radians. t is Time t since preparation, measured in fs. Keep p (Weight |c₂|² on the upper level) = 0.5; n (Upper level n) = 2 fixed. For this exercise use only 0.10625 fs ≤ t ≤ 0.42125 fs on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 0.29117734 nm, with a bounded reading uncertainty ±0.0069002 nm. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown t by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.0000315 fs, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.
MEAN POSITION ⟨x⟩ against t
Predictions from the supplied Stationary states and superpositions model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): MEAN POSITION ⟨x⟩ / nm
Horizontal axis (x): t: Time t since preparation / fs
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| t: Time t since preparation / fs | MEAN POSITION ⟨x⟩ / nm |
|---|---|
| 0.10625 | 0.1827901979436082 |
| 0.185 | 0.223165094958426 |
| 0.26375 | 0.2711729122140766 |
| 0.3425 | 0.3131583064372691 |
| 0.42125 | 0.33717895232858247 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
The model's endpoint predictions bracket the reading. Solve Y_out(t) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.
Reveal the worked solution
- Endpoint predictions are Y_out(0.10625) = 0.18279 nm and Y_out(0.42125) = 0.337179 nm. The target lies between them. On the selected branch the response is strictly increasing.
- Endpoint interpolation gives t_line = 0.10625 + (0.291177 − 0.18279)(0.42125 − 0.10625)/(0.337179 − 0.18279) = 0.327393 fs. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
- Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives t = 0.2984 fs; substituting back gives Y_out = 0.29117734 nm.
- The interpolation error in the input is |t_line − t| = 0.0289927 fs. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = 0.28427714 nm and 0.29807754 nm. Sort the roots even if the response decreases: 0.286086 fs ≤ t ≤ 0.311275 fs.
- The lower and upper input deviations are 0.0123138 fs and 0.0128748 fs. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.
Answer t ≈ 0.2984 fs; compatible interval [0.286086, 0.311275] fs. Endpoint interpolation gives 0.327393 fs.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.