Domain: Natural Science — Physics
Target concept: Electron beam in a cathode ray tube deflected by an adjacent bar magnet

Video generation prompt: In a dimly lit laboratory, an electrified cathode ray tube displayed a visible electron beam, and a hand brought a bar magnet close to it and rotated it by 180 degrees.

Evaluation guide:
(i) Target concept: Magnetic deflection of moving charges via Lorentz force in a uniform field.
Minimum mechanism: Electron beam must be charged particle stream (not light); bar magnet must generate external B-field intersecting beam path; rotation must invert B-field vector relative to beam velocity vector; deflection must be perpendicular to both v and B.
(ii)Storyline: [Phase 1: Baseline] CRT powered → straight, stable electron beam visible in dim lab. [Phase 2: Intervention] Hand enters frame holding bar magnet → magnet positioned adjacent to beam (no contact) → beam immediately begins deflecting sideways. [Phase 3: Causal Transition] Hand initiates smooth 180° rotation → beam deflection angle changes continuously → at rotation midpoint, deflection direction flips → beam settles into new steady-state path opposite original deflection. [Phase 4: Visibility Constraints] Fixed frontal view; CRT face fully in frame; beam always fully visible from origin to endpoint; magnet and hand never occlude beam entirely; lighting ensures beam glow and magnet poles remain discriminable throughout.

Manual:
Experimental Procedure
1. In a dimly lit laboratory, power on a cathode ray tube (CRT) so its electron beam is visibly glowing.
2. A hand holds a bar magnet adjacent to the CRT, near the beam path.
3. The hand rotates the bar magnet 180 degrees about its center axis while keeping it adjacent.
Observation of Experimental Phenomena
The electron beam deflects perpendicularly to its direction of motion and to the magnetic field; deflection direction reverses when the magnet is rotated 180°.
Summary of Experimental Principles
Electrons moving in a magnetic field experience the Lorentz force F = q(v × B), causing circular/helical deflection; reversing B (via 180° magnet flip) reverses F direction, thus reversing beam deflection.

Prompt Grounding rubric:
level_1: No cathode ray tube (CRT) visible; no electron beam displayed; no bar magnet present; no hand performing any action; no dimly lit laboratory setting.
level_2: CRT is present but unlit or non-emitting; OR bar magnet is present but not held by a hand; OR hand is present but not near CRT; OR lighting is bright/ambient, not dimly lit; at least two of these core objects/actions missing or misidentified.
level_3: CRT is visibly electrified and emitting a straight, continuous, faintly glowing electron beam in dim lighting; bar magnet is present and held by a hand adjacent to the CRT; hand is positioned such that magnet is clearly near the beam path; all required objects (CRT, beam, hand, magnet, dim lab) are present and correctly typed.
level_4: All elements of 3-score are present AND the hand rotates the bar magnet while maintaining adjacency to the CRT; rotation direction is visually unambiguous (e.g., clear pivot motion around vertical/horizontal axis); magnet remains fully visible throughout rotation; no object occlusion or disappearance during motion.
level_5: All elements of 4-score are present AND the magnet rotation is completed as a single, continuous, unbroken 180-degree flip (i.e., end orientation is inverted relative to start: N↔S poles swapped in visible alignment); start and end orientations are both clearly discernible (e.g., distinct pole markings or consistent asymmetry visible); no hesitation, reversal, or pause in rotation; full sequence (beam visible → magnet brought close → rotation initiated → rotation completed) occurs in correct temporal order without skipping or reordering.

Scientific and Causal Correctness rubric:
level_1: Beam shows no deflection at any time; OR beam deflects in wrong direction (e.g., toward magnet instead of perpendicular to field); OR beam vanishes, splits, flickers erratically, or changes color unrelated to deflection; OR no causal link between magnet presence/rotation and beam behavior.
level_2: Beam is present but does not change position when magnet is introduced; OR beam deflects only after magnet is removed; OR deflection occurs without magnet being adjacent; OR deflection direction contradicts right-hand rule for electron flow (e.g., beam bends parallel to field lines instead of perpendicular).
level_3: Beam visibly deflects sideways (perpendicular to both beam direction and magnet orientation) when magnet is brought adjacent; deflection magnitude changes when magnet orientation changes; beam returns to original path when magnet is withdrawn; deflection direction reverses when magnet is rotated 180°; all observed phenomena are consistent with magnetic Lorentz force on moving electrons.
level_4: All elements of 3-score are satisfied AND deflection is continuous and smooth during rotation (no jump, stutter, or discontinuity in beam position); beam position correlates monotonically with magnet orientation (e.g., maximal deflection at transverse orientation, minimal at aligned); no spurious secondary effects (e.g., beam broadening, color shift, intensity change) unrelated to Lorentz deflection.
level_5: All elements of 4-score are satisfied AND beam deflection reverses *exactly once*, precisely coincident with the midpoint of the 180° rotation (visually identifiable as the moment magnet orientation becomes orthogonal to initial state); beam path before rotation, during maximum deflection, and after full rotation are all straight, stable, and fully recoverable; no hysteresis, lag, or residual offset in beam position post-rotation.

Spatiotemporal Consistency rubric:
level_1: CRT jumps in position or scale; beam teleports or disappears/reappears abruptly; hand or magnet vanishes mid-motion; lighting shifts dramatically between frames (e.g., dim → bright → dim); CRT casing deforms or fractures; background elements flicker or warp.
level_2: CRT remains fixed but beam flickers discontinuously (≥2 frame gaps); hand motion stutters (≥2 visible pauses or direction reversals); magnet rotates jerkily with ≥2 abrupt stops; shadow positions inconsistent with light source; beam origin detaches from CRT face.
level_3: CRT is stationary and structurally intact; beam originates continuously from CRT center and maintains consistent thickness and brightness; hand moves smoothly from approach to rotation; magnet remains rigid and fully attached to hand; lighting is uniformly dim across entire scene with no frame-to-frame luminance spikes or drops; no object interpenetration or clipping.
level_4: All elements of 3-score are satisfied AND spatial relationships remain fixed: CRT–magnet distance stays approximately constant during rotation (no zoom-in/zoom-out); hand remains in same relative position to CRT; beam deflection stays confined within the visible CRT screen area (no clipping at edges); no parallax violation (e.g., magnet edge never occludes beam inconsistently across frames).
level_5: All elements of 4-score are satisfied AND motion is fully continuous: hand trajectory forms a single unbroken arc; magnet rotation is rigid-body motion (no wobble, tilt, or slippage); beam deflection sweeps smoothly along a continuous curve (no angular jumps >15° between consecutive visible positions); all shadows, highlights, and reflections maintain consistent geometry and timing with motion; zero frame-level artifacts (tearing, ghosting, strobing).