Xiomara dims an ultraviolet lamp until it delivers less than 1 J to the whole zinc plate each minute, then switches it on. By the wave model, each electron's tiny share of that trickle needs hours to build up. The first electrons leave the zinc before she lets go of the switch.
The wave model has failed once: it predicts ejection below the threshold, and none ever comes. This lesson gives it a second, independent test: the timing of the very first electron under dim light.
The wave model predicts that dim light should need a long wait before any electron gathers enough energy to leave, because in the wave model light's energy arrives continuously, spread across the whole surface, and can accumulate over time.
The dimmer the light, the less energy each electron's patch of surface receives each second, and the longer the predicted wait.
For a truly faint lamp, the predicted wait is long: minutes, or even hours.
The observation says otherwise: faint ultraviolet light ejects electrons from zinc the instant it is switched on.
No delay is ever observed, at any intensity.
Two honest predictions, two clean failures: light below the threshold should eject and never does, and dim light should eject late and instead ejects at once.
Somewhere in the wave model's picture of how light delivers energy, something is wrong. This topic ends with that question open.
A faint violet lamp, above sodium's threshold frequency, delivers only 0.5 J to a whole sodium plate each minute. How does the wave model's predicted start compare with the observed start?
By the wave model, each electron's share of 0.5 J each minute accumulates slowly, so the first ejection should come only after a long wait.
The observation: electrons leave the sodium the instant the lamp lights it.
The predicted wait never appears.
The wave model predicts a late start; the observed start is immediate. The prediction fails.
Una suggests saving the wave model: 'Maybe the electrons had already stored energy from earlier light, so they were ready to leave at switch-on.' The plate has sat in darkness for a week before the test. What happens to her suggestion?
In darkness, no light energy arrives, so no share builds up.
A plate kept dark for a week has accumulated nothing.
Yet it still ejects electrons the instant faint above-threshold light arrives.
Her suggestion fails: even a plate kept dark for a week ejects electrons immediately when faint above-threshold light arrives.
A very dim ultraviolet lamp, above zinc's threshold frequency, is about to be switched on over a zinc plate. What does the wave model predict about the first ejected electron?
For dim above-threshold light on zinc, the wave model predicts a long wait before ejection, and no delay is ever observed. What does this show?
Xiomara says: 'Faint above-threshold ultraviolet light ejects electrons from zinc with no delay, even though the wave model predicts a long wait.' Is Xiomara correct?
In the wave model, how does light's energy arrive at a metal plate?
A faint blue lamp, above potassium's threshold frequency, lights a potassium strip that has sat in darkness overnight. Electrons leave at the first instant. Why does this contradict the wave model?
Faint ultraviolet light ejects electrons from zinc the instant it switches on. Why can the wave model not explain the missing delay?