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  • General

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  • 折中

    A partially submerged black straw appears bent due to light refraction in water.

    Is this some kind of magic trick? Or is this straw really broken where it enters the water? The answer to both questions is no. There’s nothing wrong with the straw, and no magic is involved. It’s simply how light may behave when it enters a new medium .
    ::这是某种魔术吗? 还是这根稻草在进入水中的地方真的坏了? 回答这两个问题都是否定的。 稻草没有问题,也没有魔法。 光在进入新媒介时会怎样表现。

    Speed of Light and Matter
    ::轻型和物质速度

    Light always travels at the same across space. That speed, represented by the letter c, is about 300 million meters per second. However, when light travels through a medium, it travels more slowly. The speed varies for different kinds of matter. The Table gives the speed of visible light in six different materials.
    ::光总是在相同的空间穿梭。 字母c 代表的光速是每秒3亿米左右。 但是, 当光通过介质时, 光的移动速度会更慢。 不同物质的速度不同。 表格给出了六种不同材料中可见光的速度 。

    Material Speed of Visible Light (m/s)
    Air 299 million
    Water 231 million
    Glass 200 million
    Vegetable oil 150 million
    Alcohol 140 million
    Diamond 125 million

    Q: Predict the speed of visible light through vinegar.
    ::Q:通过醋预测可见光的速度。

    A: Vinegar is mostly water, so if you predicted that the speed of light through vinegar would be close to its speed through water, you are correct. The speed of visible light through Heinz® vinegar is about 230 million m/s.
    ::甲:醋主要是水,所以如果你预测通过醋的光速与水的光速接近,你就是对的。通过海因茨醋的可见光速约为2.3亿米/秒。

    Bending Light
    ::发光灯

    When light passes from one medium to another, it changes speed. For example, when light passes from air to glass, it slows down. If light strikes a sheet of glass at a 90° angle, or perpendicular to the glass, it slows down but still passes straight through the glass. However, if light enters the glass at an angle other than 90°, the light bends as it slows down. The bending of light as it changes speed in a new medium is called refraction . The Figure shows how refraction occurs. Notice that the speed of light changes again as it passes from the glass back to the air. In this case, the speed increases, and the ray of light resumes its initial direction. 
    ::当光从一个介质传到另一个介质时,光会改变速度。例如,当光从空气传到玻璃时,光会减慢速度。如果光照在90度角上击中玻璃板,或向玻璃面垂直,它会减慢速度,但还是直穿过玻璃。但是,如果光照在90度以外的角度进入玻璃时,光照会随着速度的减慢而弯曲。光照在改变新介质的速度时弯曲,则称为反射。图显示如何发生反射。请注意,光照的速度会随着从玻璃传回空气而再次变化。在这种情况下,光照的速度会加快,光线会恢复其最初的方向。

    Light rays entering and exiting glass, illustrating the concept of refraction.

    What’s Your Angle?
    ::你的角是什么?

    The angle at which light bends when it enters a different medium depends on its change in speed. The greater the change in speed, the greater the angle of refraction is. For example, light refracts more when it passes from air to diamond than it does when it passes from air to water. That’s because the speed of light is slower in diamond than it is in water.
    ::光进入不同介质时弯曲的角度取决于其速度的变化。 速度的变化越大,折射角度就越大。 比如,光从空气向钻石的折射量比从空气向水的折射量要大。 这是因为钻石的光速比水慢。

    Q: Now can you explain why the straw in the opening image appears to be broken where it enters the water?
    ::问:现在你能解释为什么开张图像中的吸管在进入水面的地方似乎被打破?

    A: The straw appears to be broken because of refraction. Light slows down and bends when it passes from the water in the glass to the air on its way to your eyes.
    ::A:稻草似乎因折射而断裂,光从玻璃中的水流到通往眼睛的空气时,会减慢和弯曲。

    In the Least Time simulation below, you can adjust the sliders so that light travels from air to a denser material like glass or diamond.  Then, drag the incident ray and refracted rays to the correct angles according to Snell’s Law . When you have found the path of least time - a red light ray will shoot out across the both materials! Very exciting!
    ::在下面最短时间的模拟中,您可以调整滑动器,让光线从空气到玻璃或钻石等更稠密的材料。 然后,根据Snell的法律,将事件射线和折射线拖到正确的角度。 当你找到最短时间的路径时, 红光线会射向两种材料! 非常令人兴奋!

    Summary
    ::摘要

    • Light always travels at the same speed through empty space. That speed, represented by the letter c, is about 300 million meters per second. However, when light travels through a medium, it travels more slowly.
      ::光总是以同样的速度在空空空空间中行走。 以字母c 表示的光速每秒约为3亿米。 但是, 当光通过介质时,光的行走速度会更慢。
    • If light passes from one medium to another at an angle other than 90 °, the light changes speed and bends. This bending of light is called refraction.
      ::如果光从一个介质向另一个介质在90°以外的角度传递,光会改变速度和弯曲。光的弯曲被称为折射。
    • The angle at which light refracts when it enters a different medium depends on its change in speed. The greater the change in speed, the greater the angle of refraction is.
      ::当光折射进入不同的介质时,光折射的角取决于其速度的变化。速度的变化越大,折射角就越大。

    Review
    ::回顾

    1. You may have heard that the speed of light is constant. Is this true? Why or why not?
      ::你可能听说光的速度是恒定的。这是真的吗?为什么或为什么不是?
    2. What is the refraction of light? When and why does it occur?
      ::什么是光线的折射?它何时和为什么发生?
    3. Draw a diagram to show how visible light refracts when it passes from air to diamond.
      ::绘制图表以显示从空气到钻石的可见光分形。