Source: https://guthlabs.ai/docs/instruments/critical-angle-total-internal-reflection-calculator/mechanism/

instrument mechanism / verified-clean

# Critical Angle / Total Internal Reflection Calculator mechanism

The inspectable method record for Critical Angle / Total Internal Reflection Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The core critical-angle formula is standard, but the specification needs an explicit angle-unit contract, the strict TIR comparison rule, validation behavior for n1<=n2, and wavelength-qualified refractive-index data. The honest label should not be n/a: the panel should state its assumptions and identify refractive indices as wavelength- and condition-dependent.

- The critical-angle formula θc=asin(n2/n1) is correct only for n1>n2, with incidence measured from the surface normal and both refractive indices dimensionless.

- The TIR decision rule is omitted: TIR occurs only when the incidence angle θi is strictly greater than θc; equality is the critical-angle case and should not be labeled TIR.

- The angle unit is unspecified. The calculator must explicitly define whether inputs and outputs use degrees or radians and convert consistently.

## Units and conventions

- n1 and n2 are dimensionless phase refractive indices at the same wavelength, temperature, and material conditions.

- n1 is the refractive index of the incident medium and n2 is the refractive index of the transmitted medium.

- Incidence angle is measured from the interface normal, not from the interface surface.

- Test vectors below use degrees unless the input key explicitly ends in _rad; asin is converted to the stated output unit.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "n1": 1.5,
    "n2": 1,
    "incidence_angle_deg": 50
  },
  "expected_outputs": {
    "critical_angle_deg": 41.8103,
    "tir": true
  },
  "working": "n2/n1 = 1.0/1.5 = 0.6666667. θc = asin(0.6666667) = 41.8103°. Compare incidence angle: 50.0° > 41.8103°, so TIR = yes."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The specification does not define handling for n1 <= n2, out-of-domain asin arguments, or signed incidence angles. Invalid-index inputs can produce undefined results, and retaining a negative incidence sign changes the TIR branch unless an unsigned-from-normal convention is enforced.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/critical-angle-total-internal-reflection-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/critical-angle-total-internal-reflection-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/critical-angle-total-internal-reflection-calculator/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`