2.3 Lens
A lens is a curved piece of transparent material
that refracts light.
A lens forms an image by refracting light rays that
pass through it.
Diverging Lens(Concave Lens)
Converging Lens(Convex Lens)
Focus
（F)
总结
Position Position
of Object of Image
u 物距
v 像距
f < v < 2f
Real
Inverted
Smaller
u = 2f
v = 2f
Real
Inverted
Same Size
f < u< 2f
v > 2f
Real
Inverted
Larger
u=f
No image
No image
u<f
f
Focal Length
f
焦距
Since light can pass through a lens in either
direction, there are two focal points for each lens.
The type of image formed by a lens depends on
the shape of the lens and the position of the
object.
Application
*2f分大小
1f分虚实
u > 2f
Focus(F)
Center of
Lens光心
Image
Camera
Projector
Same side Virtual
Magnifying
Upright
Glass
Larger
凸透镜成像总结：
2F是缩小和放大的分界点
F是实像和虚像的分界点
成实像时，物距增加，像距减小，像变小
成虚像时，物距增加，像距增加，像变大
光的反射和折射的联系
三线关系
两角关系
特殊情况
反射
折射
三线共面
三线共面
法线居中
法线居中
两角相等
空气中角大
同增同减
同增同减
垂直入射：
原路返回
垂直入射：
方向不变
2.4 Light and Color
白光由红、橙、黄、绿、蓝、靛、紫光各种
色光组成的，它是复色光。
彩虹是太阳光在传播中被空中水滴色散而产
生的。
Light can be reflected, transmitted and absorbed.
3 types of material
1) Transparent透明
e.g. water, air, clear glass……
2) Translucent半透明
e.g. wax paper, frosted glass……
3) Opaque不透明
e.g. wood, metal……
The color of a transparent or translucent object is
the color of light it reflects.
The color of an opaque object is the color of the
light it refracts.