上一片里，光打金属出电子的怪事留下了一个谜：为什么很弱的紫光行，很强的红光反而不行？答案是把光拆开看——它是一份一份的“零钱”。Last leaf, a strange thing happened when light hit metal: weak violet worked, strong red did not. The answer comes from cracking light open — it turns out light is small change, one coin at a time.
第 1 步：光是一份一份的Step 1: Light comes in packets
先别把光当水流——把它拆开，看看里面是什么。Don't treat light as a smooth stream — crack it open and look inside.
光不是连续的水流，而是一袋一袋的“零钱”：每一袋就是一个光子。小火箭把光束拆开，看到发光的小方块排着队——每袋都是光的最小一份，没法再切。Light is not a smooth stream but a bag of small change: each bag is one photon. The little rocket opened a beam and found glowing packets lined up — each one is the smallest piece of light there is.
那每一袋“零钱”值多少？爱因斯坦给出了答案：看颜色。So how much is each packet worth? Einstein gave the answer: read its colour.
第 2 步：E = hf——每袋看颜色Step 2: E = hf — each packet's value shows in its colour
每份光子的能量 E = hf：h 是普朗克常数（一张固定兑换券），f 是频率（决定颜色）。频率越高，每袋越值钱——紫光的光子是“大块头”，红光的是“小零头”。Each photon's energy is E = hf: h is Planck's constant (a fixed exchange ticket) and f is the frequency (which sets the colour). Higher frequency, heavier packet — a violet photon is a big coin, a red one a tiny coin.
那我调亮激光笔，是每袋变重了吗？So when I brighten a laser pointer, does each packet get heavier?
第 3 步：调亮 = 撒更多光子Step 3: Brighter = more photons
不是。调亮 = 撒出更多光子（袋数变多），每袋的重量一点没变。这正是上一片谜题的答案：能不能打出电子，看的是“单袋够不够重”（频率），不是“袋子有多少”（亮度）。No. Brighter means more photons fired (more packets), not heavier ones. That solves last leaf's puzzle: whether an electron gets knocked out depends on how heavy one packet is (frequency), not on how many packets arrive (brightness).
🎮 你来当发射员（30 秒）🎮 Your turn: run the emitter (30 seconds)
道理讲完了。拖频率滑块造出不同颜色的光子，拖数量滑块调亮度；再完成 4 个任务。Theory done. Drag the frequency slider to make photons of different colours, drag the count slider to change brightness — then take 4 tasks.
一句话记住它：光是一份一份的光子；每份能量 E = hf 由颜色决定，光强由数量决定。Remember it in one line: light comes as photon packets; each packet's energy is E = hf (set by colour), while brightness is just how many arrive.
光不是连续的流，而是一袋一袋的光子Light is not a smooth stream — it arrives as photon packetsE = hf：频率越高（越偏紫），每份能量越大E = hf: higher frequency (toward violet) means heavier packets调亮 = 光子数量变多，不是每份变重Brighter = more photons, not heavier ones
内容参考 OpenStax 等公开教材，多来源核对 · AI 生成、人工审核 · 发现错误欢迎指正，帮这片叶子长得更好。Based on OpenStax and other open textbooks, cross-checked across sources · AI-generated, human-reviewed · Spotted a mistake? Tell us — help this leaf grow.
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