Domain: Natural Science — Physics
Target concept: The laser beam enters the tank and is refracted at the air-water interface.

Video generation prompt: A red laser beam is incident at an oblique angle into a transparent rectangular water tank. As water is poured in, the water level gradually rises and intersects the light beam.

Evaluation guide:
(i) Target concept: Refraction of light at a planar air-water interface due to change in propagation speed.
Minimum mechanism: A collimated monochromatic light beam must cross a sharp, horizontal boundary between two optically distinct, homogeneous, isotropic media (air and liquid water), with incident angle ≠ 0°, and the observer must view the beam path through a transparent container that does not distort the interface geometry.
(ii)Storyline: [Phase 1] Empty tank + oblique red beam traversing air volume: beam appears straight and uninterrupted. [Phase 2] Water begins entering tank bottom; beam remains straight until water surface reaches beam height. [Phase 3] At first intersection, beam kinks downward at a single, well-defined point; refraction initiates. [Phase 4] Water level rises steadily; kink point migrates upward along beam path; submerged segment lengthens; bending angle increases gradually. [Phase 5] Throughout, beam remains continuous, red, and co-located with tank interior; interface stays horizontal and planar; viewpoint is fixed frontal/side, showing full beam path and interface intersection clearly; no occlusion of key region (interface zone).

Manual:
Experimental Procedure
1. Position a transparent rectangular water tank on a stable surface.
2. Direct a red laser pointer at an oblique angle so its beam enters the empty tank’s front face.
3. Slowly pour water into the tank while maintaining fixed laser position.
Observation of Experimental Phenomena
- The red laser beam is initially straight in air inside the tank.
- As water rises and first intersects the beam, the beam visibly bends downward at the air-water interface.
- As water level continues rising, more of the beam travels through water and the bend becomes more pronounced.
Summary of Experimental Principles
- Light refracts when crossing between media of different optical densities.
- At the air-water interface, the beam bends toward the normal because water has higher refractive index than air.

Prompt Grounding rubric:
level_1: No red laser beam is present anywhere in the shot, no tank is shown, and no water is poured; none of the required setup elements (laser beam, tank, or water) from the prompt ever appear on screen.
level_2: Only one of the two required objects appears (a beam with no tank, or an empty tank with no beam), or the beam clearly strikes the tank face at a near-perpendicular angle instead of an oblique one, or water is never poured in, or the water level never visibly changes; at least three of the following are missing: red beam, oblique entry angle, rectangular tank, a visible pouring action, water rising to meet the beam.
level_3: A red laser beam enters a transparent tank at an oblique angle, water is poured in, and the rising water level reaches and crosses the beam, with all steps occurring in the correct order, but at least one non-shape detail is inconsistent, such as: the beam's entry point into the tank's interior is hard to make out, the water inside the tank is faint or hard to distinguish against the tank walls, or the pouring stream itself is not visible even though the water level is visibly rising.
level_4: The beam is clearly red, the tank is a clear rectangular box with flat vertical walls, and the liquid is unmistakably water; the beam enters through a tank wall at a clearly oblique (non-perpendicular) angle; water is poured in continuously until it visibly rises above the beam's original height; the beam stays inside the tank's interior and the rising water is clearly visible filling the tank, with no missing or reordered steps.
level_5: In addition to the above, the beam stays visible for the entire clip: before the water reaches it, as it crosses it, and after; the tank keeps a consistent rectangular box shape with straight walls from the first frame to the last, without warping or wobbling; the water's top surface stays flat and horizontal as it rises rather than sloshing or curving; and the crossing point between the beam and the water surface shifts upward smoothly as the water level climbs, with no jump cuts, missing frames, or sudden repositioning of the tank or beam.

Scientific and Causal Correctness rubric:
level_1: The beam shows no reaction at all to the water: it continues in a straight line through both the air and the submerged portion with no change in direction, or there is no visible connection between the rising water level and any optical change in the beam.
level_2: The beam reacts to the water in a physically wrong way: e.g., it bends upward instead of downward, it disappears entirely at the waterline, it appears to reflect back out of the water rather than continuing into it, or it only starts bending well after the water has fully covered it rather than at first contact with the water surface.
level_3: The beam visibly kinks at the point where the rising water first touches it, and the kink bends the submerged portion downward (toward the vertical, i.e., toward the normal of the horizontal water surface) rather than upward or sideways (the qualitatively correct direction for light passing from air into water), but either the kink appears noticeably before or after the water actually reaches the beam, or the beam flickers or gaps briefly at the moment the bend appears.
level_4: The beam bends downward at the water surface at the same moment the rising water first touches it; as the water level continues to rise and more of the beam's path lies underwater, the bend becomes more pronounced (the submerged segment tilts further from the original straight-line path); the beam stays continuously red and unbroken both above and below the waterline, with no dominant reflection back into the air and no color splitting; the sequence (water contact triggering the bend, and increasing depth increasing the bend) is visually clear.
level_5: Beyond the above, the only optical change is the single downward kink at the flat, horizontal water surface: there is no rainbow-like splitting of the beam into separate colors, no faint secondary beam appearing to bounce off the tank walls, and no change in the beam's brightness or color saturation as it crosses from air into water; the bend increases smoothly and steadily as the water rises, without ever jumping abruptly to a new angle or momentarily reversing direction.

Spatiotemporal Consistency rubric:
level_1: The tank or the beam is missing for part of the clip and then suddenly shows up again; the beam jumps to a new position or angle without any visible motion connecting the two; the water level suddenly drops or jumps to a different height instead of rising continuously; the tank's walls buckle or momentarily lose their box shape; or the lighting on the tank and beam flips abruptly (e.g., the scene suddenly goes from bright to dark, or the shadow direction reverses) with nothing in the scene to explain the change.
level_2: At least one major continuity break occurs: the beam disappears on one side of the water surface and reappears on the other without a visible connecting path, the water's height jumps by a noticeable amount between frames instead of climbing gradually, the tank's edges distort noticeably while water is being poured, the beam's entry point drifts to a different spot on the tank wall partway through the clip, or the lighting/shadow on the tank shifts noticeably brighter or darker between frames without any corresponding change in the room or light source.
level_3: The tank, the beam's entry point, and the water all stay in the same relative arrangement throughout: the tank doesn't shift position, the beam keeps entering at the same spot on the tank wall, and the rising water climbs without pausing or jumping; the tank remains an intact box and the beam stays a single continuous line; a small amount of camera shake or frame-to-frame jitter is acceptable, and any cast shadow or beam brightness need not stay perfectly identical between frames as long as it does not swing back and forth or reverse abruptly.
level_4: In addition to the above, the beam shows no visible discontinuity: it doesn't flicker on and off or change thickness or brightness abruptly; the water's surface rises at a steady, uniform pace rather than speeding up, stalling, or stuttering between frames; the tank's corners and edges stay crisp and well-defined throughout the pour; and the camera viewpoint does not drift or shift in a way that changes where the beam, tank, or water surface appear relative to each other.
level_5: Beyond the above, the beam shows no flicker, pulsing, or change in thickness at any point; the rise of the water surface reads as a smooth, constant-speed motion rather than speeding up, slowing down, or momentarily freezing; the tank keeps a rigid rectangular form with no visible breathing, warping, or blurred edges; and any cast shadow or highlight on the tank and beam shifts gradually and consistently as the water rises, rather than jumping abruptly or reversing direction.