University Physics I · topic UPI-EXT-WS.02
Sinusoidal wave functions and phase
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.
Further practice
Work through a fresh case before tackling the extension.
Sinusoidal Wave Functions & Phase: predict a finite change
A sinusoidal travelling wave is a disturbance y(x, t) = A sin(kx − ωt + φ₀) that depends on position and time only through the phase kx − ωt + φ₀, so the same sine pattern repeats every λ = 2π/k in space and every T = 2π/ω in time. Use the supplied topic model Y_out = 2*pi/lam, where Y_out is WAVE NUMBER k = 2π/λ (rad m⁻¹). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. lam is Wavelength λ, measured in m. Keep t (Time t) = 0.4 s; dir (Direction of travel (−1 or +1)) = 1 fixed. For this exercise use only 1.31875 m ≤ lam ≤ 3.68125 m 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. Calculate Y_out at lam = 1.8385 m and 2.16925 m. Find the signed output change ΔY_out and the average sensitivity ΔY_out/Δlam across this interval. State whether the response increases or decreases; distinguish this interval average from a derivative at one point.
WAVE NUMBER k = 2π/λ against lam
Predictions from the supplied Sinusoidal Wave Functions & Phase 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): WAVE NUMBER k = 2π/λ / rad m⁻¹
Horizontal axis (x): lam: Wavelength λ / m
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| lam: Wavelength λ / m | WAVE NUMBER k = 2π/λ / rad m⁻¹ |
|---|---|
| 1.31875 | 4.764500706866037 |
| 1.909375 | 3.290702615871469 |
| 2.5 | 2.5132741228718345 |
| 3.090625 | 2.0329821014130105 |
| 3.68125 | 1.7068075537329945 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
Substitute each value of lam separately while keeping every other input fixed, then subtract in the same order.
Reveal the worked solution
- At lam = 1.8385 m, substitute into Y_out = 2*pi/lam: Y₀ = 3.41756 rad m⁻¹.
- At lam = 2.16925 m, the same fixed-parameter model gives Y₁ = 2.89648 rad m⁻¹.
- Signed change: ΔY_out = Y₁ − Y₀ = -0.521082 rad m⁻¹; the input change is Δlam = 0.33075 m.
- Average sensitivity is ΔY_out/Δlam = -1.57546 rad m⁻¹ per m. Its negative sign means that this response decreases over the specified interval.
- This is a secant slope between two settings. It equals a point derivative only for a locally linear relation or in a justified small-interval limit.
Answer Y₀ = 3.41756 rad m⁻¹, Y₁ = 2.89648 rad m⁻¹; ΔY_out = -0.521082 rad m⁻¹; average sensitivity = -1.57546 rad m⁻¹ per m.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.
Extra challenging questions
Work through the linked stages and explain what each result means.
Sinusoidal Wave Functions & Phase: infer an input with uncertainty
A sinusoidal travelling wave is a disturbance y(x, t) = A sin(kx − ωt + φ₀) that depends on position and time only through the phase kx − ωt + φ₀, so the same sine pattern repeats every λ = 2π/k in space and every T = 2π/ω in time. Use the supplied topic model Y_out = 2*pi/lam, where Y_out is WAVE NUMBER k = 2π/λ (rad m⁻¹). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. lam is Wavelength λ, measured in m. Keep t (Time t) = 0.4 s; dir (Direction of travel (−1 or +1)) = 1 fixed. For this exercise use only 1.31875 m ≤ lam ≤ 3.68125 m 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 = 2.2766195 rad m⁻¹, with a bounded reading uncertainty ±0.085472 rad m⁻¹. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown lam by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.00023625 m, 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.
WAVE NUMBER k = 2π/λ against lam
Predictions from the supplied Sinusoidal Wave Functions & Phase 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): WAVE NUMBER k = 2π/λ / rad m⁻¹
Horizontal axis (x): lam: Wavelength λ / m
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| lam: Wavelength λ / m | WAVE NUMBER k = 2π/λ / rad m⁻¹ |
|---|---|
| 1.31875 | 4.764500706866037 |
| 1.909375 | 3.290702615871469 |
| 2.5 | 2.5132741228718345 |
| 3.090625 | 2.0329821014130105 |
| 3.68125 | 1.7068075537329945 |
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(lam) = 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(1.31875) = 4.7645 rad m⁻¹ and Y_out(3.68125) = 1.70681 rad m⁻¹. The target lies between them. On the selected branch the response is strictly decreasing.
- Endpoint interpolation gives lam_line = 1.31875 + (2.27662 − 4.7645)(3.68125 − 1.31875)/(1.70681 − 4.7645) = 3.24099 m. 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 lam = 2.75988 m; substituting back gives Y_out = 2.2766195 rad m⁻¹.
- The interpolation error in the input is |lam_line − lam| = 0.481115 m. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = 2.1911475 rad m⁻¹ and 2.3620915 rad m⁻¹. Sort the roots even if the response decreases: 2.66001 m ≤ lam ≤ 2.86753 m.
- The lower and upper input deviations are 0.0998657 m and 0.107657 m. 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 lam ≈ 2.75988 m; compatible interval [2.66001, 2.86753] m. Endpoint interpolation gives 3.24099 m.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.