来自《耶鲁大学开放课程：新生有机化学 第5集 第5集》

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  and the reason is because you're measuring the phase
  这是为了方便大家观察相位变化
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  perpendicular to different directions of the wave.
  特别是沿着垂直波形传播的方向
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  That's just to help you out, if you try this and have --
  如果你们刚才没有听懂
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  and are confused by that.
  可以下载这个帮助你理解
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  Okay, now there are --
  好了 现在思考下一个问题
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  so suppose you have just an arbitrary set of electrons,
  假设你有一系列的电子
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  and the waves coming in and hitting them,
  光波入射进来 与电子碰撞
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  what directions will you get reinforcement in?
  在哪个角度可以观察到增强?
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  Well, there are two directions that you're guaranteed,
  有两个角度 是一定可以观察到的
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  no matter what the spacing is
  无论电子间距大小
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  and that's this.
  如图所示
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  Here the light comes in and goes out.
  光波入射进来 再出射