Domain: Natural Science — Physics
Target concept: Propagation of Light in Inhomogeneous Media

Video generation prompt: A transparent rectangular container is filled with a stratified sucrose solution (low concentration in the upper layer and high concentration in the lower layer), forming a stable density gradient. A green laser beam is incident horizontally from the side of the tank, passing through the density gradient layer. A white screen is placed behind the tank to enhance the visibility of the light path, and the experimental environment is dimmed.

Evaluation guide:
(i) Target concept: Light ray curvature in a vertically graded refractive index medium.
Minimum mechanism: The medium must exhibit a monotonic, stable vertical refractive index gradient (higher below, lower above), and the incident ray must be initially horizontal, enabling continuous refraction via Snell’s law applied differentially across layers.
(ii)Storyline: Frame 1–2: Static wide shot showing upright transparent container, dim ambient, green laser source aligned at mid-height on left side. Frame 3–6: Beam enters container → immediately begins downward curving trajectory (no straight segment) → curvature intensifies progressively toward bottom → exits container near lower-right edge. Frame 7–10: Curved beam projects onto white screen behind, forming a single, unbroken, smoothly downward-bending luminous trace: fully visible, co-located with beam exit point, with no secondary reflections or scattering artifacts. Perspective is fixed frontal-side view: container fully in frame, laser source partially visible left-of-center, screen fully visible right-of-center; all elements coplanar and aligned in same depth plane.

Manual:
Experimental Procedure
1. Place a transparent rectangular container upright on a stable surface.
2. Fill it with a stratified sucrose solution: low concentration at top, high at bottom — forming a stable vertical density gradient.
3. In a dimmed room, direct a green laser beam horizontally from the side, entering the container midway in height.
4. Position a white screen directly behind the container to capture the transmitted light path.
Observation of Experimental Phenomena
The green laser beam bends smoothly and continuously downward as it passes through the container, tracing a curved path on the white screen — not a straight line.
Summary of Experimental Principles
Light propagates along curved paths in inhomogeneous media due to gradual refractive index change; here, increasing sucrose concentration downward increases local refractive index, causing continuous downward refraction (governed by Fermat’s principle and ray optics in graded-index media).

Prompt Grounding rubric:
level_1: None of the required setup elements appear together: no transparent rectangular tank holding liquid, no green laser entering from the side of the tank, no white screen behind the tank, and no dimmed room; the shot looks like an unrelated scene or is missing the apparatus entirely.
level_2: Only part of the setup is shown: a tank, a green beam, or a screen appears alone rather than together; for example the tank has no liquid inside, the laser enters from above or head-on instead of from the side, the screen is missing or placed in front of the tank instead of behind it, or the room is brightly lit rather than dimmed.
level_3: A transparent rectangular tank filled with liquid is shown; a green laser beam enters horizontally from one side of the tank; a white screen stands behind the tank to catch the transmitted light; the room is dim enough that the beam and its trace on the screen stand out clearly.
level_4: Everything at the 3-point level is present, and further: the tank stands upright with its flat rectangular face toward the camera; the laser visibly comes from a source mounted at the side of the tank near its mid-height rather than from above or below; the screen is flat, upright, and sits directly behind the tank rather than off to one side; nothing blocks the view of the tank, beam, or screen.
level_5: Everything at the 4-point level is present, and further: the tank's edges and corners look crisp and its liquid looks clear apart from the intended layering; the beam is a thin, unbroken green line where it enters the tank; the screen is evenly lit and blank except for the beam's trace, filling the background with no visible gaps; the dim room shows no stray lamps, windows, or glare reflecting off the tank or screen.

Scientific and Causal Correctness rubric:
level_1: The green beam passes straight through the tank with no bending at all, or the beam is not green, or there is no sign whatsoever that the layered sucrose solution is affecting the light's path.
level_2: The beam is green and enters horizontally, but it stays straight the whole way through the tank, or it curves upward instead of downward, or it disappears partway through the liquid, or the screen shows only a static bright dot instead of a stretched, curved trace.
level_3: The green beam enters horizontally from the side and bends smoothly downward as it crosses the tank, staying visible the whole way through the liquid, while the screen shows a continuous curved streak of light aligned with where the beam exits the tank.
level_4: Everything at the 3-point level holds, and further: the bending is downward only, never upward or side to side; the beam stays one continuous line rather than splitting or flickering out partway; the screen shows a single clean curved streak rather than multiple spots or scattered glare.
level_5: Everything at the 4-point level holds, and further: the downward bend starts as soon as the beam enters the liquid, without any straight stretch first; the curve deepens gradually and smoothly from top to bottom rather than bending in sudden jumps; the beam keeps a steady thickness and brightness along its curved path; the curved streak on the screen lines up with the beam's actual exit point and direction.

Spatiotemporal Consistency rubric:
level_1: The tank suddenly changes position, size, or shape between frames; the laser beam appears or disappears without any visible travel through space; the screen jumps to a different location; or the dim lighting flips abruptly between bright and dark.
level_2: At least one clear continuity problem shows up: the beam seems to start in mid-air with no visible source, the tank shifts slightly between shots, the screen is absent for part of the video and then appears, the bright spot on the screen jumps to a new location without the beam visibly moving there, or the room's lighting noticeably brightens or dims partway through.
level_3: The tank stays in the same spot and keeps its rectangular shape the whole time; the laser source and the beam's entry point stay fixed; the beam's path changes smoothly from one frame to the next with no jump or freeze; the screen stays in place and fully visible; the dim lighting stays steady without flickering.
level_4: Everything at the 3-point level holds, and further: the tank's walls never bulge, warp, or wobble; the beam's brightness changes gradually if it changes at all, rather than snapping on or off; any highlight or reflection on the tank or screen stays on the same side and at the same strength throughout, consistent with one fixed light source and a fixed camera.
level_5: Everything at the 4-point level holds, and further: the beam's downward curve looks smooth and continuous across the whole video rather than jumping between distinct shapes from frame to frame; the tank's edges and the screen's surface stay visually clear and stable without shimmering or flickering; the curved streak of light on the screen tracks continuously with the beam from when it first appears through to the final frame, with no gaps or duplicate traces.