Domain: Natural Science — Physics
Target concept: Corona Discharge

Video generation prompt: In a darkroom environment, the positive terminal of the high-voltage power supply is connected to a sharp metal needle, while the negative terminal is connected to a circular metal plate, with a distance of 10 cm between them. The voltage is gradually increased within the darkroom.

Evaluation guide:
(i) Target concept: Localized gas ionization at a sharp electrode under high DC electric field in ambient air, below sparking threshold.
Minimum mechanism: Air must be present at atmospheric pressure; needle must be geometrically sharp (radius of curvature < 100 µm implied by visual acuity); electric field at tip must exceed ~3 MV/m to initiate ionization; voltage polarity must be positive on needle to produce visible corona (negative corona is dimmer and less stable in air).
(ii)Storyline: Frame 1–2: Static shot of darkroom with needle and plate in fixed positions, wires connected, power supply off (no glow). Frame 3–4: Voltage adjustment begins (dial turns/meter rises); no glow yet. Frame 5–6: First appearance of faint, fuzzy violet–blue glow localized strictly at needle tip. Frame 7–8: Glow intensifies: expands radially from tip, increases brightness and density, remains non-bridging. Frame 9–10: Glow stabilizes at higher intensity; plate remains dark and uninvolved; no spark forms. Throughout: fixed viewpoint, no occlusion, no motion of objects, no lighting change except glow emission.

Manual:
Experimental Procedure
1. Place sharp metal needle and circular metal plate 10 cm apart in a completely dark room.
2. Connect needle to positive terminal of high-voltage power supply using red wire; connect plate to negative terminal using black wire.
3. Gradually increase voltage while observing needle tip.
Observation of Experimental Phenomena
A faint violet–blue glow appears exclusively at the sharp tip of the needle when voltage reaches corona threshold; glow intensifies with further voltage increase but does not bridge the gap to the plate.
Summary of Experimental Principles
Corona discharge occurs at regions of high electric field gradient — such as sharp points — where air ionizes locally without full dielectric breakdown; the violet–blue color arises from nitrogen emission bands in ionized air.

Prompt Grounding rubric:
level_1: The high-voltage power supply, the sharp metal needle, or the circular metal plate is missing, or none of the three appear together; or the room is clearly not dark (window light, ceiling fixtures, or daylight-like illumination is visible); or the needle and plate show no visible wiring connecting them to the supply at all.
level_2: At least one of the three objects (needle, plate, power supply) is visible and the room looks dim, but something core is wrong: the needle is blunt rather than sharp, the plate is not circular, the polarity of the terminals cannot be told apart, or the wires appear to float without actually touching the objects.
level_3: All three objects (the high-voltage supply with visible + and − terminals, the sharp needle, and the circular plate) are present; the room is confirmed dark with no ambient light; the needle and plate are clearly separated by a gap consistent with the stated 10 cm spacing; but which wire goes to which terminal (needle vs. plate, positive vs. negative) is not visually clear.
level_4: All three objects are present and correctly shaped; the room stays dark throughout; the needle is visibly wired to the positive terminal and the plate to the negative terminal (e.g., distinguishable wire colors or terminal labels); the needle-to-plate gap stays visually constant at roughly the stated 10 cm separation with no overlap or contact; the camera keeps both needle and plate in view together the whole time.
level_5: Everything needed for a 4-point score is present, and beyond that: the needle-to-positive / plate-to-negative wiring never changes or becomes ambiguous for the entire video; neither object is ever blocked from view, swapped, or moved to a new position; the dark room shows no stray light, reflection, or visible object anywhere outside the glow itself, from the first frame to the last.

Scientific and Causal Correctness rubric:
level_1: No violet-blue glow appears anywhere near the needle at any point; there is no light emission from the needle tip as voltage rises; turning the voltage dial or watching the meter rise has no visible effect on the scene.
level_2: A flicker of light appears somewhere in the frame, but it is not centered on the needle tip (it might appear on the plate, along the needle shaft, or in the wiring), and it does not track with the voltage being increased; or the glow color is clearly wrong (e.g., white, green, or orange instead of violet-blue).
level_3: A violet-blue glow appears only at the sharp tip of the needle as the voltage is turned up, staying off the shaft, the plate, and the wires; the glow's appearance roughly lines up with the voltage being raised (dial turning or meter climbing), though the timing between the two feels loose or the glow pulses on and off unevenly.
level_4: The violet-blue glow stays confined to the needle tip and visibly grows brighter and larger only as the voltage keeps increasing; it never appears on the plate, wires, or needle shaft; it does not appear before the voltage starts rising or after it levels off; and at no point does the discharge turn into a spark or arc jumping across the gap.
level_5: Everything needed for a 4-point score is present, and beyond that: the glow looks like a proper corona (a soft, fuzzy, halo-like patch at the tip rather than a hard-edged beam), and it never bridges the gap to the plate; as voltage climbs, the glow's growth from a faint spot to a fuller halo reads as one continuous strengthening rather than sudden jumps in size or brightness, and no stray light appears anywhere else in the scene at any time.

Spatiotemporal Consistency rubric:
level_1: The needle, plate, or power supply vanishes and reappears at a different spot without any transition; the dark room suddenly turns bright like daylight partway through; the camera cuts or spins for no reason tied to the experiment; or the glow appears before the needle is even shown wired up.
level_2: The needle or plate changes size or angle inconsistently between shots; the glow switches on or off abruptly with no fade in or out; the wires appear to detach and reattach without anyone touching them; or the dark background suddenly reveals texture, clutter, or a stray light source that wasn't there before.
level_3: The needle and plate stay roughly where they should be with only a slight, easy-to-miss wobble; the glow occasionally dims for a moment during the voltage increase in a way that looks like a brief hiccup rather than a clean buildup; the dark background stays black overall but has some faint graininess that comes and goes.
level_4: The needle tip and plate stay fixed in their positions and orientation relative to each other for the whole video; the glow only ever starts and grows at the needle tip, with a smooth onset rather than snapping into view; the dark background stays evenly black with no visible flicker; the wiring and terminals never shift or change appearance.
level_5: Everything needed for a 4-point score holds, and in addition: the glow's growth from a faint spark to a fuller, brighter halo looks like one smooth, continuous strengthening rather than any stutter, blink, or sudden jump in size; the needle, plate, and wiring stay crisp and steady in the same spot from the first frame to the last; nothing in the scene besides the glow itself ever brightens, dims, or shifts.