Kenji shines a strong red floodlight on a clean zinc plate all afternoon, and not one electron leaves the plate. A faint ultraviolet lamp ejects electrons from the same plate the moment it switches on.
In the photoelectric effect topic, you saw four observations break the wave model. In the photon model topic, the photon explained all four. This lesson files that whole story on one side of the evidence: the photoelectric effect is the light behavior that only the photon model explains.
A metal has a threshold frequency. Below it, no electrons leave, no matter how intense the light is and no matter how long it shines.
No wave picture explains that. A wave would deliver its energy in a steady stream that builds, so intense light of any frequency should eventually eject electrons. It never does.
The photon model explains it directly. An electron escapes only if a single photon, on its own, delivers enough energy to free it. Below the threshold frequency, every photon is too weak.
The same pattern runs through all four observations: whole lumps, one per electron, with more energy per lump at higher frequency.
Could a wave picture explain any of the four? No. A steady, spread-out delivery of energy makes no threshold, no instant start, and no tie between frequency and electron energy.
This lesson and the last one are a pair. Interference and diffraction: only the wave model. The photoelectric effect: only the photon model. Light shows both kinds of behavior, and the next lesson names that.
Bright green light shines on a polished nickel plate for an hour and ejects nothing. Faint ultraviolet light ejects electrons from the same plate at once. Which model of light explains this pair of results?
Green light sits below nickel's threshold frequency, so no green photon on its own carries enough energy to free an electron. Brightness only adds more photons that are each too weak.
Ultraviolet light sits above the threshold, so one ultraviolet photon frees an electron the moment it is absorbed.
A wave delivering energy steadily would do neither: it would eject with bright green light eventually, and it would start slowly under faint light.
Only the photon model explains the pair of results.
Soraya reads that doubling a lamp's brightness doubles how many electrons leave a metal each second, while each electron's maximum energy stays unchanged. Which side of the evidence does this belong to?
Doubling the brightness doubles how many photons arrive each second, and each photon's energy stays the same, because frequency sets it.
More photons eject more electrons each second, and the energy any one electron can get from its one photon is unchanged.
A wave picture would pour more energy onto every electron under brighter light, raising electron energies. That is not what happens.
This belongs on the particle side: the photon model explains it.
Which light behavior can only the photon model explain?
A copper plate ejects electrons under faint ultraviolet light the instant the lamp switches on. Which model of light explains the missing delay?
Soraya says: 'If light were only a wave, bright light of any frequency would eventually eject electrons from a metal, and that is not what happens.' Is Soraya correct?
A metal ejects no electrons below its threshold frequency, however bright the light. Why does this observation support the photon model?
A metal plate sits under very faint light that is above its threshold frequency. Electrons start leaving the instant the light arrives. Which statement explains why there is no delay?
Which pairing of evidence to model is right?