# Public teacher-targeted worked guide · Physics Days 1–10

This file is **publicly accessible by URL**. [Check A/B](../STUDENT-CHECKS.md) are fresh relative to practice but **not secure exams**, QCAA instruments or a certified unit result. Separate `physics explanation`, `calculation/unit and assumption`, and `claim boundary` in feedback; also log source access, response mode, calculator, time and any content hint. Use “clear in this response / partial or hinted / not yet evidenced” only as a next-teaching note, not a QCAA achievement judgment. All figures and objects are invented. No real experiment or safety claim is supported.

## Daily worked models and next actions

| Day | Source-bound answer | Next move when evidence is thin |
| --- | --- | --- |
| 01 | Same material and phase at **60 °C** supports the same model average particle kinetic-energy state, not equal total internal energy. A **1.00 kg** sample contains five times the mass of a **0.20 kg** sample; the equal-size drawing is not to scale. Do **not** state a joule value or an exact energy ratio without more assumptions/reference data. | Ask “per particle average or whole sample?”; place MASS beside each bowl. |
| 02 | The continuous solid bridge connects higher and lower model temperatures, so **conduction** is a possible energy path without bulk metal movement. There is no transfer-rate or safe-touch evidence. | Trace a path through named material; ask what the sketch did not measure. |
| 03 | In the stipulated diagram, **air** moves in the proposed loop and energy is transferred by **convection**. The **23 °C** lower and **27 °C** upper labels do not by themselves measure flow direction or speed; “warmth rises as a substance” is misleading. | Make separate AIR MOTION and ENERGY TRANSFER arrows; mark the proposed arrow as modelled. |
| 04 | **Thermal radiation** can cross the evacuated gap. Conduction and convection cannot act **through that empty gap** because there is no matter there; a solid support elsewhere could conduct if supplied. The received fraction/rate is unknown. | Keep the qualifier “through the gap”; ask for a receiver/property measurement before power claims. |
| 05 | The constructed crate can include conduction **through the wall**, convection **within moving air**, and radiation **between facing surfaces**. A diagram supplies no food temperature, time or food-safety proof. | Assign a different named location to each mechanism and remove *proven safe*. |
| 06 | QCAA rounded convention: `22+273=295 K`; `−5+273=268 K`. Final minus initial is **−27 K**; equivalently a **27 K decrease**. A temperature **interval** is not given another +273. The exact SI offset is 273.15, beyond this stated syllabus convention. | Convert each temperature first, then subtract; remove degree sign from K and keep the decrease direction. |
| 07 | `27.0−18.0=9.0 °C`. With **stipulated ±0.1 °C for each reading**, a conservative worst-case difference bound is **±0.2 °C**, so `ΔT=(9.0±0.2) °C`. Percentage bound `0.2/9.0×100≈2.2%`. Decimal display alone does not establish calibration accuracy or eliminate common bias. | Ask where the ±0.1 came from (the note, not the last digit); put uncertainty next to the **difference** before dividing. |
| 08 | `Q=mcΔT`: `0.50 kg×2,000 J kg⁻¹ K⁻¹×4 K=4,000 J`; `1.00 kg×2,000×4=8,000 J`. In the stipulated single-phase/no-loss model, doubling mass doubles Q at fixed c and ΔT. No heater rating or actual loss is known. | Cancel kg and K; hold c/ΔT constant on both rows. |
| 09 | `ΔT=Q/(mc)`. Aster: `3,000 J/(0.50 kg×1,000 J kg⁻¹ K⁻¹)=6 K`; Beryl: `3,000/(0.50×2,000)=3 K`. Same energy and mass, different stipulated c; no real tile safety follows. | Check which variable changed, then point to c in the denominator. |
| 10 | From `(1 K,1,000 J)` and `(3 K,3,000 J)`, `slope=ΔQ/ΔT=2,000 J/2 K=1,000 J K⁻¹`. Since `slope=mc`, `c=1,000 J K⁻¹/0.25 kg=4,000 J kg⁻¹ K⁻¹`. The four points are calculated in a no-loss, constant-c, single-phase range; they cannot prove a universal or experimental relationship. | Distinguish line slope from c by dividing by mass; ask whether any points were measured (no). |

## Check A worked response · light-box route map

The fictional designer addresses gallery visitors. *All* and *never* enlarge a diagram into an untested performance/safety promise. The **evacuated gap** has no air: **thermal radiation** can travel from emitting panel toward receiver through it, but **air convection cannot operate through that gap**. **Conduction** can occur along the touching **solid bracket**; **convection** can occur in moving air of the **outer air-filled housing** if its proposed flow occurs. The arrow is a model, not an observation. A suitable correction is: “The invented diagram permits a radiation path across the evacuated gap, a solid-bracket conduction path and a proposed outer-air convection path. It provides no temperature, heat-rate or safety measurement.”

**Next moves:** If the learner puts convection in the gap, ask them to locate matter there. If they say no conduction anywhere, point to the touching bracket. If they present *safe* as a result, ask for temperature, time, receiving-surface and operating-condition data; do not improvise a real test.

## Check B worked response · gallery-board model line

Using `(2 K,800 J)` and `(6 K,2,400 J)`, slope `ΔQ/ΔT=(2,400−800) J/(6−2) K=1,600 J/4 K=**400 J K⁻¹**`. In `Q=mcΔT`, slope is **mc**, not c. Divide by sample mass: `c=400 J K⁻¹/0.40 kg=**1,000 J kg⁻¹ K⁻¹**`. The public caption omits the 0.40 kg mass and generalises beyond the four **calculated** points. A bounded replacement is: “For this fictional 0.40 kg single-phase no-loss model over 0–6 K change, Q rises by 400 J per kelvin, corresponding to model c = 1,000 J kg⁻¹ K⁻¹. No real-material or wider-range result was measured.”

**Next moves:** If `400` is reported as specific heat capacity, ask what mass has to be divided out. If the unit is `J/K` for c, use the `Q=mcΔT` unit cancellation. If the learner calls the points experimental, return to the source's *calculated model* label and missing uncertainty bars.

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