Domain: Natural Science — Physics
Target concept: Photoelectric Effect

Video generation prompt: A vacuum phototube is connected to a microammeter, with a variable-frequency ultraviolet light source placed on the left and a zinc cathode on the right. The frequency of the light source is gradually increased from below to above the threshold frequency of the zinc plate, while keeping the light intensity constant.

Evaluation guide:
(i) Target concept: Threshold-frequency-dependent photoelectron emission from zinc cathode under monochromatic UV illumination in vacuum.
Minimum mechanism: Vacuum environment prevents electron scattering; zinc cathode must be clean metallic surface; incident photons must be absorbed (not reflected) to eject electrons; microammeter must be in series to detect net charge flow.
(ii)Storyline: Frame 1–3: Static wide shot showing full setup: UV source (left), phototube (center, transparent glass, zinc cathode visible inside right end), microammeter (right, wired to phototube terminals), frequency dial visible on source. Frame 4–6: Frequency cue advances (dial rotates right / spectral bar shifts right); needle motionless. Frame 7–8: Cue crosses threshold marker; needle begins smooth rightward sweep. Frame 9–10: Cue continues advancing; needle sweeps further, no reversal or pause. Viewpoint: Fixed frontal orthographic angle, no cuts, no occlusion, full visibility of cathode, dial, and needle throughout.

Manual:
Experimental Procedure
1. Place variable-frequency UV light source on left, vacuum phototube centered, zinc cathode inside right end of phototube, microammeter connected to phototube terminals.
2. Keep light intensity constant. Gradually increase light frequency from below to above zinc’s threshold frequency.
3. Observe microammeter needle deflection.
Observation of Experimental Phenomena
- Needle remains at zero while frequency is below threshold.
- Needle begins deflecting only after frequency exceeds threshold.
- Deflection increases continuously as frequency rises further.
Summary of Experimental Principles
- Photoelectric effect requires incident photon energy (hν) ≥ work function (Φ) of zinc.
- Below threshold frequency (ν₀ = Φ/h), no photoelectrons emitted → zero current.
- Above ν₀, photoelectrons ejected → current detected by microammeter.

Prompt Grounding rubric:
level_1: The vacuum phototube, the microammeter, the UV light source, or the zinc cathode is missing entirely; or the pieces appear in the wrong relative arrangement: for example the light source on the right, the cathode on the left, or the meter not wired to the tube; or there is no visible indication that the light's frequency is changing over time.
level_2: Most of the four pieces (phototube, microammeter, UV source, zinc cathode) are present, but at least two are positioned incorrectly: for example the cathode isn't visible inside the tube, or the meter isn't clearly wired to the tube's terminals; or the frequency change is only implied by on-screen text rather than shown through a dial, color shift, or similar visual cue.
level_3: The UV source sits on the left, the phototube is centered with the zinc cathode visible inside its right end, and the microammeter is wired to the tube's terminals; the light's brightness looks constant throughout; the frequency increase is shown through at least one visible cue, such as a rotating dial or a spectrum bar shifting toward shorter wavelengths.
level_4: Everything in the 3-point level holds, and in addition every piece keeps its position for the whole clip (the source stays on the left, the cathode stays inside the tube, the meter stays wired), the frequency cue advances smoothly without ever jumping backward, and nothing extraneous blocks the view of the cathode, dial, or needle.
level_5: Everything in the 4-point level holds, and in addition the frequency cue is visually anchored to the light source itself (for example the dial is mounted on the source housing, or the color shift clearly originates from the source's aperture), the needle and dial markings stay legible throughout, and the cathode remains fully visible inside the tube with no part of the setup ever cut off by the frame edge.

Scientific and Causal Correctness rubric:
level_1: The needle deflects before the frequency has increased at all, or it deflects while the light source appears off, or it never deflects even once the frequency clearly exceeds the labeled threshold.
level_2: The needle moves at the lowest frequency shown, before any threshold marker is reached, or its deflection grows steadily from the very start rather than beginning only once the threshold cue is passed.
level_3: The needle stays at zero while the frequency cue is still below the marked threshold, then starts deflecting once the cue visibly passes that threshold point; the cathode looks like plain metal throughout, with no unexplained glow.
level_4: Everything in the 3-point level holds, and in addition the deflection keeps increasing or holding steady once past the threshold rather than dropping back to zero or stalling, and the needle never moves backward or resets while the frequency cue remains above the threshold.
level_5: Everything in the 4-point level holds, and in addition the needle's very first movement lines up closely with the frame where the frequency cue crosses the threshold marker (not noticeably before or after), and the cathode never shows any glow or heat-related change that would suggest a non-photoelectric cause.

Spatiotemporal Consistency rubric:
level_1: A piece of the setup (the source, tube, meter, or cathode) disappears and reappears, the needle jumps to a new angle with no visible sweep leading up to it, the camera cuts or pans partway through the clip, the light source flickers erratically or goes dark and back on, or the phototube's glass visibly cracks or changes shape.
level_2: The light source shifts position noticeably between shots, the meter looks disconnected and then reconnected, the tube's glass visibly bulges or ripples, or the needle freezes for a couple of frames and then jumps sharply to a new angle.
level_3: The source, tube, cathode, and meter all stay in their same places throughout; the needle's motion looks continuous, without freezing or jumping; the shadows cast by the phototube and light source housing don't swing to a new angle partway through the clip; the tube's glass doesn't warp or flicker in transparency.
level_4: Everything in the 3-point level holds, and in addition the needle sweeps at a visually even pace rather than lurching or stalling, the light source's brightness looks steady rather than flickering, and there is no camera shake, zoom, or refocus during the clip.
level_5: Everything in the 4-point level holds, and in addition the needle, dial markings, and cathode all stay clearly and consistently rendered without shimmering or warping, and the connections between the tube's terminals and the meter's wires look stable and unbroken across the whole clip.