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SCIENCE · INVESTIGATE AND EXPLAIN

Separate an angular baseline from wavelength dependence

A measured deviation angle may contain both refraction and an instrument zero error. For a thin prism at small angles, the supplied first-order relation is δ≈(n−1)A, where A is prism apex angle and n the refractive index relative to the surrounding air approximation. A common angular readout offset adds a constant. All angles must use a consistent unit in this first-order relation.

Learning outcome: Fit red index and angular offset from two records, freeze the third-angle prediction and then reveal it. Compare the separately supplied blue prediction and state which additional wavelength observation would actually test dispersion. Explain why a red-only fit is insufficient for that claim.

Starting recap

Use normal-based angles, signed conjugate distances and explicit optical-path/reflection phases. Separate geometric direction, amplitude and energy; preserve focal and critical boundaries.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

At reference angle4° and offset+.1°, red indications at4° and8° are2.1° and4.1°. Their difference recovers nred−1=.5 and offset+.1°. The unused12° prediction is6.1° within the first-order model. The independently supplied blue index predicts2.26° at4°, a blue-minus-red difference.16°.

Open the experiment

Predict

What can two red readings at known distinct prism angles identify in this model?

Experiment

Fit red index and angular offset from two records, freeze the third-angle prediction and then reveal it. Compare the separately supplied blue prediction and state which additional wavelength observation would actually test dispersion. Explain why a red-only fit is insufficient for that claim.

Separate angle baseline from dispersion evidence

Worked teaching model · synthetic values · Supplied thin-prism first-order law delta=(n−1)A for small angles, plus common angular offset. Red index1.50 and separately supplied blue index1.54. Red records at A and2A calibrate nred and offset; red3A is fresh validation of this approximate law. Blue index is not inferred from red-only data.

Reset keeps your prediction, captures and practice history.

Thin-prism calibration and unused red comparison

indicated deviation (degrees)prism angle (degrees)0126.10

Unlike graph quantities rescale independently; read units and values, not screen angles. 1: red fit from first two angles (solid).2: fresh red third-angle record (filled markers).3: blue using separately supplied dispersion (filled markers). Joined curves show the supplied model, not additional observations.

Equivalent numerical coordinates for Thin-prism calibration and unused red comparison

red fit from first two angles

prism angle (degrees)indicated deviation (degrees)
00.1
0.150.175
0.30.25
0.450.325
0.60.4
0.750.475
0.90.55
1.050.625
1.20.7
1.350.775
1.50.85
1.650.925
1.81
1.951.075
2.11.15
2.251.225
2.41.3
2.551.375
2.71.45
2.851.525
31.6
3.151.675
3.31.75
3.451.825
3.61.9
3.751.975
3.92.05
4.052.125
4.22.2
4.352.275
4.52.35
4.652.425
4.82.5
4.952.575
5.12.65
5.252.725
5.42.8
5.552.875
5.72.95
5.853.025
63.1
6.153.175
6.33.25
6.453.325
6.63.4
6.753.475
6.93.55
7.053.625
7.23.7
7.353.775
7.53.85
7.653.925
7.84
7.954.075
8.14.15
8.254.225
8.44.3
8.554.375
8.74.45
8.854.525
94.6
9.154.675
9.34.75
9.454.825
9.64.9
9.754.975
9.95.05
10.055.125
10.25.2
10.355.275
10.55.35
10.655.425
10.85.5
10.955.575
11.15.65
11.255.725
11.45.8
11.555.875
11.75.95
11.856.025
126.1

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

fresh red third-angle record

prism angle (degrees)indicated deviation (degrees)
126.1

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

blue using separately supplied dispersion

prism angle (degrees)indicated deviation (degrees)
42.26

At most 82 representative computed coordinates including endpoints; the plotted curve can use a finer grid. A table of a revealed generator is not independent measurement evidence.

Calculated quantities under the declared measurement model
QuantityValueUnit
First red angle indication2.1degrees
Second red angle indication4.1degrees
Inferred red refractive index1.5ratio
Recovered angular offset0.1degrees
Fresh red third-angle indication6.1degrees
Predicted red third-angle indication6.1degrees
Blue indication from independently supplied index2.26degrees
Blue-minus-red indication at first prism angle0.16degrees

A common angular offset cancels in differences; dispersion still needs wavelength-dependent evidence.

The first-order thin-prism relation is delta=(n−1)A. Two red records at A and2A identify slope nred−1 and additive baseline within that approximate model;3A is an unused prediction. A blue index supplied independently gives stronger deviation here. Red-only data cannot infer the blue index or a full dispersion curve. At a stationary interface frequency stays fixed while wavelength becomes lambda0/n; the changed direction is not a changed source frequency.

Predict before inspecting the values. Save contrasting records with assumptions and one alternative explanation. This virtual display does not certify practical measurement technique.

A common angular offset cancels in differences; dispersion still needs wavelength-dependent evidence.

The first-order thin-prism relation is delta=(n−1)A. Two red records at A and2A identify slope nred−1 and additive baseline within that approximate model;3A is an unused prediction. A blue index supplied independently gives stronger deviation here. Red-only data cannot infer the blue index or a full dispersion curve. At a stationary interface frequency stays fixed while wavelength becomes lambda0/n; the changed direction is not a changed source frequency.

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Define the optical model

A measured deviation angle may contain both refraction and an instrument zero error. For a thin prism at small angles, the supplied first-order relation is δ≈(n−1)A, where A is prism apex angle and n the refractive index relative to the surrounding air approximation. A common angular readout offset adds a constant. All angles must use a consistent unit in this first-order relation.

Build the signed account

Red observations at known angles A and2A fit two parameters: their difference divided by A gives nred−1, and the first reading then gives the offset. A fresh red observation at3A tests that fitted approximate law. It must not be silently used to improve the fit and still called validation. Finite prism angles, oblique incidence, imperfect geometry and changing offsets could explain a residual; fitting a straight line is not proof of exact thin-prism behavior.

Test the limits and evidence

Dispersion means the material index depends on frequency. Here nred=1.50 and nblue=1.54 are separately supplied premises, so blue bends more in the stated normal-dispersion example. Red-only data cannot establish the blue index or a whole spectral curve. At a stationary interface the frequency remains fixed while wavelength becomes λ0/n. The later color separation is not the prism changing every photon into a new source frequency. No physical prism or bright-source measurement is requested.

Worked original case

At reference angle4° and offset+.1°, red indications at4° and8° are2.1° and4.1°. Their difference recovers nred−1=.5 and offset+.1°. The unused12° prediction is6.1° within the first-order model. The independently supplied blue index predicts2.26° at4°, a blue-minus-red difference.16°.

Predict and investigate

Fit red index and angular offset from two records, freeze the third-angle prediction and then reveal it. Compare the separately supplied blue prediction and state which additional wavelength observation would actually test dispersion. Explain why a red-only fit is insufficient for that claim.

Changed-case practice

Try the changed case before feedback

Red indications at prism angles2° and4° are1.3° and2.3°. Find the inferred red refractive index.

This practice is public and unsaved. A matching number does not verify understanding. Retain your explanation, assumptions and changed-case evidence in the separate course workspace.

Sources and boundaries

Original text and numerical cases checked 30 October 2026 against the primary explanation. All optical activity is virtual: no laser, sunlight viewing, eye exposure, physical lens alignment or device construction is requested. Public feedback is not independent mastery; retain first calculations, critique and changed-case evidence in the separate course workspace.

Derive the first-order premise instead of treating it as exact

Inside a triangular prism the two internal refraction angles satisfy r1+r2=A, while the geometric deviation is δ=i+e−A. For small angles in radians, Snell law gives i≈nr1 and e≈nr2, so δ≈(n−1)A. The common angular conversion means the final linear relation can consistently use degrees too. Predict/check: at n=1.5, doubling a small A doubles this leading deviation. Large angles need the sine relations rather than this linear scaling; an exact fit to generated first-order records cannot establish its real-world accuracy.

Apply

What can two red readings at known distinct prism angles identify in this model?

Public practice checks a specific claim. It does not establish independent mastery.

Which independent observation would reject the approximation, sign convention or calibration premise rather than merely refit it?

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

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