Domain: Natural Science — Physics
Target concept: Sublimation

Video generation prompt: A small amount of solid iodine is placed in a sealed transparent glass tube, which is heated at one end using a water bath at 50°C.

Evaluation guide:
(i) Target concept: Sublimation and deposition of iodine as a pure solid-gas phase transition under mild heating.
Minimum mechanism: Iodine must remain thermodynamically stable (no decomposition), have sufficient vapor pressure at 50°C to sublime, and exhibit temperature-gradient-driven vapor transport and cold-surface nucleation, all without melting (melting point = 113.7°C > 50°C).
(ii)Storyline: [Phase 1: Setup] Sealed transparent tube enters frame containing discrete purple-black iodine crystals at one end; water bath (warm, translucent liquid) occupies lower portion of frame; tube end makes stable contact with bath surface. [Phase 2: Initiation] Within first 2–3 seconds, purple-violet vapor emerges *only* from heated end; no vapor elsewhere. [Phase 3: Transport] Vapor flows directionally along inner tube wall toward cooler end, visible as semi-transparent, diffusing cloud with increasing density near destination. [Phase 4: Deposition] Vapor contacts cooler tube wall and transforms directly into new shiny, dark crystals, appearing progressively, not instantaneously. [Perspective/Visibility] Fixed frontal or slightly angled view; entire tube remains fully in frame; no occlusion of iodine, vapor path, or deposition zone; lighting reveals crystal luster and vapor translucency without glare or loss of detail.

Manual:
Experimental Procedure
1. Place a small amount of solid iodine (purple-black crystals) inside a sealed transparent glass tube.
2. Position the tube horizontally so one end contacts a water bath maintained at 50°C.
3. Observe for 10 seconds.
Observation of Experimental Phenomena
Purple-violet vapor forms at the heated end, migrates toward the cooler end, and condenses into shiny dark crystals there. No liquid phase appears.
Summary of Experimental Principles
Iodine undergoes sublimation (solid → gas) at 50°C due to its high vapor pressure; vapor travels via diffusion/convection and re-deposits (deposition) on cooler surfaces — a reversible phase transition without passing through liquid state.

Prompt Grounding rubric:
level_1: None of the three required elements are visible (no sealed transparent glass tube, no solid iodine crystals, and no water bath), and no heating action of any kind is shown.
level_2: Only one of the three required elements appears (for example, a glass tube by itself, or a water bath by itself, or a loose purple-black powder with no tube around it), and it is shown in the wrong form: an open or unsealed tube, an opaque tube, molten/liquid iodine, or iodine granules with no vessel; nothing is placed against anything and no heating is depicted.
level_3: A sealed transparent glass tube, a small quantity of purple-black solid iodine crystals inside it, and a water-bath container holding visibly warm water are all present at once; the iodine sits inside the tube, and one end of the tube touches the water bath; no vapor, color change, or other sign that heating is doing anything is required at this level.
level_4: Everything required at the 3-point level is present, and in addition the tube lies horizontal or close to horizontal with the heated end clearly immersed in or pressed against the water bath, the iodine crystals sit bunched at the heated end of the tube at the very start, and the frame contains nothing extraneous: no hands, no unrelated lab tools, no second container.
level_5: Everything required at the 4-point level is present, and in addition the arrangement never changes across the clip: the tube stays in the same place and fully visible, the iodine (and later, the vapor and any new crystals) stays inside the tube the whole time, the water bath shows no splashing, overflow, or boiling of its own, and nothing is ever cut out of frame or moved to a new spot.

Scientific and Causal Correctness rubric:
level_1: The iodine shows no change at all in color, texture, or state and stays static throughout, or the iodine visibly melts into a liquid pool; either outcome is wrong, since at 50°C iodine (melting point 113.7°C) should sublime directly to vapor rather than stay inert or liquefy.
level_2: A gas-like haze does appear, but it is not the purple-violet color characteristic of iodine vapor (e.g., it is white steam, a colorless shimmer, or gray smoke), or the haze shows up at the cool end rather than originating at the heated end, or vapor is already visible before the tube ever touches the water bath.
level_3: Purple-violet vapor forms at the heated end and travels along the tube toward the cooler end, where it turns directly into new solid crystals; at no point does a liquid iodine phase appear, and the iodine that lands at the cool end stays solid rather than pooling or running.
level_4: Everything required at the 3-point level holds, and in addition the vapor stream is continuous rather than flickering on and off, comes only from the region in contact with the water bath, and visibly builds up as fresh crystal deposits at the cool end; nothing simultaneously melts, bubbles, or discolors the glass.
level_5: Everything required at the 4-point level holds, and in addition the whole cause-and-effect chain reads clearly on screen: vapor only starts after the tube contacts the water bath, the vapor's visible density builds up gradually rather than jumping to full haze at once, the new crystals forming at the cool end show the same dark purple-black, lustrous look as the original iodine, and at no point does anything suggest liquid iodine, a chemical reaction with the glass, or decomposition of the iodine.

Spatiotemporal Consistency rubric:
level_1: The tube instantly relocates or reorients between frames with no visible motion; the tube visibly cracks, bends, or warps out of its rigid glass shape; the iodine, the vapor, or the newly formed crystals vanish completely in one frame and reappear differently in the next; the water-bath container itself changes shape or position without cause; or the overall lighting on the scene switches abruptly, as if two different shots were spliced together.
level_2: The tube's tilt or position visibly rotates or shifts by more than roughly 15 degrees partway through the clip without any corresponding cause; the vapor's direction of travel reverses or jumps sideways without the tube's contact point changing; the shadow the tube casts swings to a new direction mid-clip even though nothing about the light source changes; or crystals appear at the cool end noticeably before any vapor has visibly traveled there.
level_3: The tube shows a small, noticeable wobble (a jitter under roughly 5% of the frame height) but does not relocate; the vapor's visible thickness pulses up and down in a way that doesn't track a smooth heating progression, though the shot itself stays unbroken; there is a brief, visible pause between the vapor reaching the cool end and crystals starting to appear, but everything remains within one continuous take; the tube's cast shadow stays pointed in the same direction throughout.
level_4: Everything required at the 3-point level holds, and in addition the vapor drifts toward the cool end smoothly rather than in sudden bursts or reversals, the new crystals build up gradually rather than snapping to full coverage in a single frame, and the tube stays in the same position relative to the water bath for the entire clip with no visible jump cuts or skipped motion.
level_5: Everything required at the 4-point level holds, and in addition the clip reads as one uninterrupted, physically coherent shot: the framing never snaps between different viewpoints, the timing of the vapor's advance lines up with when the new crystals actually appear at the cool end, and there is no moment where the tube, the bath, or the crystal deposits appear to double, warp, or flicker in a way a viewer would notice without specialized tools.