章节大纲

  • A baby touching her reflection in a mirror, appearing as two identical images.

    What does this picture show? Is it a photo of identical twin sisters, or is it just one girl looking in a mirror? The picture shows a single girl and her mirror image.
    ::这张照片显示什么?是同性姐妹的照片,还是只有一个女孩照镜子?图片显示的是单身女孩和她的镜像。

    How Mirrors Form Images
    ::镜镜如何形成图像

    A mirror is typically made of glass with a shiny metal backing that reflects (almost) all the light that strikes it. When a mirror reflects light, it forms an image. An image is a copy of an object that is formed by or . Mirrors may have flat or curved surfaces. The shape of a mirror’s surface determines the type of image it forms. For example, some mirrors form real images, and other mirrors form virtual images. What’s the difference between real and virtual images?
    ::镜子通常由玻璃制成,有闪亮的金属背面,反映(几乎)撞击它的所有光线。当镜子反光时,它形成图像。图像是由或由镜子组成的物体的复制件。镜子可能有平面或弯曲的表面。镜子表面的形状决定着它形成的图像类型。例如,有些镜子形成真实的图像,而另一些镜子则形成虚拟图像。真实图像和虚拟图像有什么区别?

    • A real image forms in front of a mirror where reflected light rays actually meet. It is a true image that could be projected on a screen.
      ::真实的图像形式在镜子前, 反光光线实际相遇。 它是一个真实的图像, 可以在屏幕上放映 。
    • A virtual image appears to be on the other side of the mirror. Of course, reflected rays don’t actually go through the mirror to the other side, so a virtual image doesn’t really exist. It just appears to exist to the human brain.
      ::虚拟图像似乎在镜子的另一面。 当然,反射线实际上并没有穿过镜子到另一面,因此虚拟图像其实并不存在。 它似乎只是存在于人的大脑中。

    Q: Look back at the image of the girl pointing at her image in the mirror. Which type of image is it, real or virtual?
    ::问:看看那个女孩在镜子中指着她的形象。是什么样的图像,是真实的还是虚拟的?

    A: The image of the girl is a virtual image. It appears to be on the other side of the mirror from the girl.
    ::A:女孩的形象是虚拟形象,似乎在镜子的另一面,从女孩身上。

    Plane Mirror
    ::平面镜镜

    The mirror in the opening photo is a plane mirror. This is the most common type of mirror. It has a flat reflective surface and forms only virtual images. The image formed by a plane mirror is also right-side up and life sized. But something is different about the image compared with the real object in front of the mirror. Left and right are reversed. Look at the girl brushing her teeth in the Figure  . She is using her right hand to brush her teeth, but her image (on the left) appears to be brushing her teeth with the  left hand. All plane mirrors reverse left and right in this way. The term mirror image refers to how left and right are reversed in an image compared with the object.
    ::开张照片中的镜子是平面镜子。 这是最常见的镜像。 它有一个平面反射面, 并且只形成虚拟图像。 平面镜子所塑造的图像也是向右侧的, 并且有生命的大小。 但是图像与镜子前的真实对象相比有些不同。 向左和向右反转。 看看图中刷牙的女孩。 她正在用她的右手刷牙, 但她( 左边的) 的图像似乎正在用左手刷牙。 所有平面镜子都以这种方式向左和向右反转。 术语反射图像是指在图像中向左和向右的图像与对象的反转。

    A girl brushing her teeth with a toothbrush in a bathroom mirror.

    In the simulation below, the young man is getting ready for the Prom. He needs to stand at a particular and have the mirror be a particular length to be able to view his entire body.  Rays of light are emerging from various light sources in the room and bouncing off him into the mirror. Play around with rays from different locations, try different mirror lengths, and see what you can discover about the reflection of light in a plane mirror:  
    ::在下面的模拟中,年轻人正在准备参加Prom。 他需要站在一个特定的位置上,让镜子有一个特定的长度来观察他的整个身体。 光线正在从房间里的各种光源中涌现出来,然后跳进镜子中。 玩弄不同地点的光线,尝试不同的镜体长度,看看你能从一个平面镜中看到什么光的反射:

     

    Concave Mirror
    ::集中镜像

    Some mirrors have a curved rather than flat surface. Curved mirrors can be concave or convex . A concave mirror is shaped like the inside of a bowl. This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. The focal point is the point in front of the mirror where the reflected rays meet. You can see how concave mirrors form images in the Figure  . Concave mirrors are used behind car headlights. They focus the light and make it brighter. Concave mirrors are also used in some telescopes. 
    ::有些镜像的表面是弯曲的,而不是平面的。曲线的镜像可以是圆形的,也可以是圆形的,也可以是圆形的。圆形的镜像的形状像碗内一样。这种镜像的形状是真实的或虚拟的,取决于对象相对于焦点的位置。焦点是反射射线相交的镜子前面的点。您可以看到图中圆形的镜像是如何形成图像的。圆形的镜像在车头灯后面使用,它们集中光线,使之更亮。一些望远镜中也使用圆形的镜像。

    Light ray reflection in a concave mirror illustrating image formation and focal point.

    Convex Mirror
    ::Convex 镜像

    The other type of curved mirror, a convex mirror, is shaped like the outside of a bowl. Because of its shape, it can gather and reflect light from a wide area. As you can see in the Figure  , a convex mirror forms only virtual images that are right-side up and smaller than the actual object. 
    ::另一种曲线反射镜是卷曲反射镜,形状像碗的外表。由于其形状,它可以收集和反射大面积的光线。从图中可以看到,卷曲反射镜只形成与实际对象相近和小于实际对象的虚拟图像。

    Light rays reflecting off a convex mirror, illustrating virtual images formation.

    Q: Convex mirrors are used as side mirrors on cars. You can see one in the Figure  . Why is a convex mirror good for this purpose?
    ::问题:Convex镜像被用作汽车的侧面镜。您可以看到图中的镜像。为什么曲面镜像对此有用?

    A: Because it gathers light over a wide area, a convex mirror gives the driver a wider view of the area around the vehicle than a plane mirror would.
    ::A:由于光线在宽广的区域收集光,一个阴道镜像使驾驶员能够比飞机镜镜更宽广地观察车辆周围的区域。

    Convex side mirror showing wider view of road and vehicles, with cautionary text.

    When light enters a Cassegrain telescope from a distant planet, first it bounces off a concave primary mirror and then off a secondary convex mirror. Play around with a Cassegrain Telescope in the simulation below and see if you can until you get a clear view of Jupiter in the eyepiece:
    ::当光从遥远的行星进入卡塞克雷纳望远镜时, 光首先从熔岩主镜中反弹, 然后从二次孔面镜中反弹。 在下面的模拟中, 用卡塞克雷纳望远镜玩耍, 看看能不能看清楚木星的眼镜 :

     

     

    Watch the video below to learn more about how ray diagrams can be used to predict how an the image of an object will appear when reflected in a mirror:
    ::观察下面的视频, 以了解如何使用射线图来预测一个物体的图像在镜子中映射时会如何出现:

     

     

    Summary
    ::摘要

    • When a mirror reflects light, it forms an image. An image is a copy of an object formed by reflection (or refraction). A real image is a true image that forms in front of a mirror where reflected light rays actually meet. A virtual image appears to be on the other side of the mirror and doesn’t really exist.
      ::当镜子反射光时,它会形成图像。图像是反射(或反射)形成的物体的复制件。真正的图像是真实的图像,在反光光线实际相遇的镜子前形成。 虚拟图像似乎在镜子的另一面,实际上不存在。
    • Most mirrors are plane mirrors that have a flat reflective surface. A plane mirror forms only virtual, right-side up, and life-sized images.
      ::大多数镜子都是平面反射面平面的平面镜子。平面镜只形成虚拟的、右侧的和寿命大小的图像。
    • A concave mirror is shaped like the inside of a bowl. The type of image it forms depends on where the object is relative to the focal point. The image may be real, upside down, and reduced in size; or it may be virtual, right-side up, and enlarged.
      ::混凝土镜子的形状像碗的内形。 它所形成的图像类型取决于对象与焦点的相对位置。 图像可能是真实的, 颠倒的, 缩小的; 或者可能是虚拟的, 右侧的, 并放大的 。
    • A convex mirror is shaped like the outside of a bowl. It forms only virtual images that are right-side up and reduced in size relative to the object. 
      ::凸形镜像碗外形。 它只形成与对象相对的右侧和缩小大小的虚拟图像 。

    Review
    ::回顾

    1. What is an image? How do real and virtual images differ?
      ::什么是图像? 真实图像和虚拟图像有何不同?
    2. Define the focal point of a mirror.
      ::定义镜像的焦点 。
    3. Describe the image formed by a plane mirror.
      ::描述由平面镜子形成的图像 。
    4. What type of image is formed by a concave mirror if the object is between the mirror and the focal point?
      ::如果对象介于镜像和焦点之间, 凝聚镜像会形成什么样的图像 ?
    5. Mirrors like the one in the Figure  are sometimes placed at street intersections so drivers can see around blind corners. What type of mirror is used for this purpose? What type of image does it form?
      ::图中的镜像有时被放置在街交叉路口,这样司机就能在盲角周围看到。为此目的,什么类型的镜像?它会形成什么样的图像?

    A convex mirror mounted on a wall reflecting a street scene and vehicles.