Domain: Engineering — Chemical Engineering
Target concept: Impressed Current Cathodic Protection

Video generation prompt: Set up an external current cathodic protection system, connecting the iron block to the negative terminal of a DC power supply as the cathode, and a graphite electrode as the auxiliary anode. Both electrodes were immersed in a 3% sodium chloride solution with a distance of 10 cm between the two electrodes. The power supply was turned on, and the current was adjusted to 10 mA. The setup was continuously photographed for 24 hours.

Evaluation guide:
(i) Target concept: Electrochemical suppression of iron corrosion via forced cathodic polarization using an external DC source and inert anode.
Minimum mechanism: Iron must be electrically isolated from anode except via external circuit; electrolyte must conduct ions; anode must be electrochemically stable (graphite does not dissolve); cathode reaction (oxygen reduction or water reduction) must dominate over iron oxidation; observable consequence is zero iron dissolution/rusting and exclusive anodic gas evolution.
(ii)Storyline: Frame sequence must show: (1) static setup with both electrodes immersed and wired before power-on; (2) power supply activation (visible indicator or label change); (3) immediate onset of bubbles *only* at graphite surface; (4) sustained absence of any change on iron surface; (5) continuous coexistence of all elements in fixed spatial configuration. Viewpoint must be fixed frontal mid-shot showing full container, both electrodes, and power supply terminals; no cutaways, no close-ups, no occlusion of connections or electrode surfaces.

Manual:
Experimental Procedure
1. Place iron block and graphite electrode side-by-side in transparent container filled with clear liquid.
2. Connect iron block to negative terminal of DC power supply using insulated wire.
3. Connect graphite electrode to positive terminal of same power supply using insulated wire.
4. Turn on power supply.
Observation of Experimental Phenomena
- Iron block remains unchanged: no rust, no bubbles, no color shift.
- Graphite electrode remains intact: no erosion, but fine bubbles form continuously on its surface.
- Liquid stays clear and colorless; no precipitation or cloudiness.
Summary of Experimental Principles
External current cathodic protection forces iron to become cathode, halting oxidation (rusting); graphite acts as inert auxiliary anode where chloride oxidation and oxygen evolution occur.

Prompt Grounding rubric:
level_1: No iron block, no graphite electrode, no DC power supply, no sodium chloride solution container, or none of the required objects appear in the video.
level_2: At least one correct object appears (e.g., iron block OR graphite electrode OR power supply OR container), but no two objects are simultaneously present in the same scene, and no connection or immersion is shown.
level_3: All four core objects are present in the same scene: iron block, graphite electrode, DC power supply, and a transparent container holding liquid; iron block is visibly connected via wire to the negative terminal, graphite electrode is visibly connected to the positive terminal, and both electrodes are fully immersed in the liquid.
level_4: All conditions for score 3 are satisfied, AND the wiring polarity is visually unambiguous: negative-terminal wire connects exclusively to iron block, positive-terminal wire connects exclusively to graphite electrode, and no reversed or crossed connections appear.
level_5: All conditions for score 4 are satisfied, AND the iron block and graphite electrode are positioned side-by-side within the same liquid-filled container with fixed spatial proximity (both fully submerged, no floating, no contact between electrodes), and the power supply unit is visibly powered (e.g., active indicator light or labeled ON state visible).

Scientific and Causal Correctness rubric:
level_1: No scientifically plausible electrochemical phenomenon occurs: e.g., iron block shows vigorous bubbling, rapid rusting, color change, or dissolution; or graphite electrode shows corrosion, disintegration, or discoloration inconsistent with inert anode behavior.
level_2: At least one electrode exhibits a phenomenon inconsistent with cathodic protection: e.g., iron block shows visible orange-brown rust formation during operation, OR graphite electrode shows visible crumbling or black residue shedding into solution.
level_3: Iron block remains visually unchanged (no rust, no color shift, no surface pitting or bubbling), AND graphite electrode remains visually unchanged (no erosion, no dark residue, no structural deformation), AND liquid remains clear and colorless throughout the video.
level_4: All conditions for score 3 are satisfied, AND no gas evolution (bubbles) appears at the iron block surface, while occasional fine bubbles appear *only* at the graphite electrode surface, and never elsewhere.
level_5: All conditions for score 4 are satisfied, AND bubble generation is spatially exclusive: bubbles appear *only* at graphite electrode surface, persist continuously during operation, and show no cessation or migration; iron block surface remains perfectly smooth, metallic-gray, and completely bubble-free for entire duration.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal violation: electrodes teleport between frames, container changes shape/size/orientation abruptly, liquid level fluctuates discontinuously, or wires disconnect/reconnect without motion continuity.
level_2: Moderate violation: at least one electrode shifts position without visible motion (jump-cut relocation), OR wire connections appear/disappear between frames, OR lighting/shadow changes abruptly across frames without cause.
level_3: All objects maintain fixed relative positions: iron block and graphite electrode remain side-by-side in same container throughout; wires remain taut and continuously connected; liquid surface remains stable and horizontal; no object flickers, vanishes, or reappears.
level_4: All conditions for score 3 are satisfied, AND motion is physically coherent: if bubbles appear, their rise is vertically upward from graphite surface only, with consistent size and spacing; no lateral drift, no merging, no spontaneous generation away from electrode.
level_5: All conditions for score 4 are satisfied, AND temporal continuity is perfect: no frame duplication, no frozen frames, no skipped motion; all visual elements evolve smoothly, including bubble detachment cycle (formation → growth → release → rise), with no stutter, jump, or interpolation artifacts.