| English | 意味 |
|---|---|
| diffraction/dɪˈfrækʃn/ | 回折 |
You hear around corners, but you can't see around them
- Someone talks in the next room and you hear them, even without a straight line to your ear.
- Yet you can't see around the same corner. Why the difference?
- Waves bend and spread as they pass through gaps and around edges — diffraction 衍射.
- How much they spread depends on the gap size compared with the wavelength.
Waves spread through gaps
- When a wave passes through a gap or past an edge, it fans out into the space beyond.
- This spreading is diffraction, and it happens for all waves.
- Straight (plane) waves become curved as they emerge from a narrow gap.
- It is why sound reaches you around a doorway or a wall.
回折とは：
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
回折とは、波がスリットや端を通るときに広がる現象である。
回折は、波がスリットを通るか、____ を回り込むときに生じる。
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
波はスリットや端で広がる。
Gap size matters most
- Diffraction is greatest when the gap is about the same size as the wavelength.
- A gap much wider than the wavelength barely spreads the wave.
- A gap around the wavelength's size spreads it almost in a semicircle.
- So a narrow gap (relative to $\lambda$) causes the most bending.
回折が最大になるのはスリット幅が：
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
スリットが波長と同じ大きさのとき、広がりは最大である。
回折に関する正しい記述をすべて選択せよ。
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
回折は波を広げ、スリット幅 ≈ 波長の場合に最大となり、音が角を曲がる理由でもある。巨大なスリットは回折が最小である。
Why sound bends but light doesn't (usually)
- Sound has a wavelength of about a metre, similar to doorways — so it diffracts strongly.
- Light's wavelength is tiny (under a micrometre), so everyday gaps barely diffract it.
- That's why you hear around corners but light casts sharp shadows.
- Shrink a slit to light's wavelength, though, and light diffracts too (next lesson).
回折は多いか少ないか？
スリット幅が波長と同程度の場合、波は最も広がる。各ケースを分類せよ。
音はスリットサイズと同程度の波長を持つため、ドア開口部周辺で強い回折を示す。
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
音のメートル単位の波長は日常のスリットサイズと一致するため、強い回折を示す。
なぜ光は通常、日常のスリット通過時にシャープな影を作るのか？
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
光の波長は極めて小さいため、日常のスリットは光を十分に回折させるにはあまりにも大きい。
Diffraction is strongest when the gap width is comparable to the wavelength, not when the gap is huge. This is exactly why sound (long wavelength) diffracts around everyday obstacles but light (tiny wavelength) usually doesn't — the gap is far larger than light's wavelength.
Sound (wavelength ~$1\ \text{m}$) and light (wavelength ~$5\times10^{-7}\ \text{m}$) both pass through a $1\ \text{m}$ doorway.
- The doorway ≈ the sound wavelength, so sound diffracts strongly — you hear around it.
- The doorway is millions of times the light wavelength, so light barely diffracts.
Diffraction is the spreading of waves through gaps and around edges. It is greatest when the gap ≈ the wavelength. Because sound has a metre-scale wavelength it diffracts around everyday obstacles, while light's tiny wavelength means it usually casts sharp shadows.