The Photoelectric Effect · 光电效应
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| photoelectric effect/ˌfəʊtəʊɪˈlektrɪk ɪˈfekt/ | 光电效应 | guāng diàn xiào yìng |
Blue light knocks electrons out — red light never does, however bright
- Shine light on a metal and electrons can fly off. But there's a catch.
- Blue light ejects them instantly; red light does nothing — even blindingly bright red.
- No wave theory can explain that. Only photons can.
- This is the photoelectric effect 光电效应, Einstein's proof that light is made of particles.
蓝光能打出电子——红光却永远不行,无论多亮
- 用光照射金属,电子会飞出来。但有一个玄机。
- 蓝光瞬间打出它们;红光什么也不做——即使亮得刺眼。
- 没有波动理论能解释这一点。只有光子能。
- 这就是光电效应,爱因斯坦证明光由粒子构成的证据。
One photon, one electron
- Light delivers energy in photons, each carrying $E = hf$.
- To escape the metal, an electron needs one photon with enough energy in a single hit.
- A photon below a threshold frequency simply doesn't have enough energy — no electron leaves.
- Above the threshold, each photon knocks out one electron.
一个光子,一个电子
- 光以光子传递能量,每个携带 $E = hf$。
- 要逃出金属,电子需要一个具有足够能量的光子一次击中。
- 低于阈值频率的光子根本没有足够能量——没有电子离开。
- 高于阈值,每个光子打出一个电子。
The photoelectric effect is evidence that light behaves as: · 光电效应证明光表现为：
A threshold frequency can only be explained if light comes in photons. · 只有当光是由光子组成时，才能解释阈值频率。
Why brightness doesn't help below threshold
- If the frequency is too low, even a very bright beam won't eject any electrons.
- More photons of too-little energy each still can't free an electron — brightness gives quantity, not quality.
- Above threshold, a brighter beam ejects more electrons (more photons), but not faster ones.
- Only raising the frequency gives each electron more kinetic energy.
为什么低于阈值时亮度无济于事
- 如果频率太低,即使非常亮的光束也打不出任何电子。
- 更多能量太小的光子,每一个仍无法释放电子——亮度给的是数量,而非质量。
- 高于阈值,更亮的光束打出更多电子(更多光子),但不是更快的。
- 只有提高频率才给每个电子更多动能。
Below the threshold frequency, increasing the brightness of the light: · 低于阈值频率时，增加光的亮度：
Below threshold, each photon is too weak — brightness cannot free any electrons. · 低于阈值时，每个光子太弱——亮度无法释放任何电子。
Above threshold, a brighter beam ejects: · 高于阈值时，更亮的光束射出：
More photons eject more electrons; speed depends on frequency, not brightness. · 更多光子射出更多电子；速度取决于频率而非亮度。
The energy balance
- Some photon energy goes into freeing the electron (the work function); the rest becomes its kinetic energy.
- In symbols: $hf = \phi + \text{KE}_{\text{max}}$.
- So above threshold, higher frequency → faster ejected electrons.
- This exact accounting is what earned Einstein the Nobel Prize.
能量平衡
- 一部分光子能量用于释放电子(逸出功);其余变成它的动能。
- 用符号:$hf = \phi + \text{KE}_{\text{max}}$。
- 所以高于阈值时,更高的频率 → 更快的出射电子。
- 正是这精确的账目让爱因斯坦获得诺贝尔奖。
The photoelectric effect · 光电效应
The maximum kinetic energy of ejected electrons rises linearly with the light's frequency, above a threshold. · 被射出电子的最大动能随光频率线性增加，前提是超过阈值。
Above the threshold, higher-frequency light ejects electrons with more kinetic energy. · 高于阈值时，更高频率的光射出具有更多动能的电子。
$hf = \phi + \text{KE}_{\text{max}}$: more photon energy leaves more kinetic energy. · $hf = \phi + \text{KE}_{\text{max}}$: 更多的光子能量留下更多的动能。
The minimum energy needed to free an electron from the metal is the ____ function. · 从金属中释放电子所需的最小能量是 ____ 函数。
The work function $\phi$ is the energy to free an electron; the rest becomes kinetic energy. · 逸出功 $\phi$ 是释放电子所需的能量；其余部分转化为动能。
Select all · 所有 true statements about the photoelectric effect. · 选择关于光电效应的所有正确陈述。
A threshold frequency, particle behaviour, and frequency-set speed all hold. Bright red (below threshold) ejects nothing. · 阈值频率、粒子行为和频率决定速度均成立。明亮的红光（低于阈值）不射出任何东西。
Below the threshold frequency, no electrons are ejected — no matter how bright the light. Brightness (more photons) can't substitute for frequency (energy per photon). A wave theory expects bright light to always work; the fact that it doesn't proves light is particles.
低于阈值频率,没有电子被打出——无论光多亮。亮度(更多光子)不能替代频率(每个光子的能量)。波动理论预期亮光总能起作用;它不起作用这一事实证明光是粒子。
Dim ultraviolet light ejects electrons from a metal, but intense red light does not. Why?
- UV photons are above the threshold frequency (enough energy each), so they eject electrons.
- Red photons are below it — each is too weak, and adding more (brighter) doesn't help.
暗淡的紫外光能从金属打出电子,但强烈的红光不能。为什么?
- 紫外光子高于阈值频率(每个能量足够),所以它们打出电子。
- 红光光子低于它——每个都太弱,加更多(更亮)也无济于事。
The photoelectric effect: light ejects electrons only above a threshold frequency, because energy arrives in photons ($E = hf$) that must free an electron one at a time. Below threshold, brightness doesn't help; above it, higher frequency gives faster electrons ($hf = \phi + \text{KE}_{\text{max}}$). It proves light is particles.
光电效应:光只在高于阈值频率时打出电子,因为能量以光子($E = hf$)到达,必须一次释放一个电子。低于阈值,亮度无济于事;高于它,更高的频率给出更快的电子($hf = \phi + \text{KE}_{\text{max}}$)。它证明光是粒子。