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教育头条 > 初中物理 > 八年级物理上册|第五章 透镜及其应用知识点总结

八年级物理上册|第五章 透镜及其应用知识点总结

初中物理 07-23 浏览量: 分享:
学习如逆水行舟,不进则退,很多人赢在了假期,也有很多人输在了假期。暑假已经开始了,三好网小编为大家整理了八年级物理上册|第五章 透镜及其应用知识点总结,一起来学习。

 
透镜及其应用
 
一、透镜
1.凸透镜:
远视镜(老花镜)片,中间厚,边缘薄叫做凸透镜。
2.凸透镜对光线的作用
凸透镜对光线有会聚作用。
平行于主光轴的光射到凸透镜上,其折射光线会聚在焦点上。
3.凹透镜:
近视镜片,中间薄,边缘厚,叫做凹透镜。
4.凹透镜对光线的作用:
凹透镜对光线有发散作用。
平行于主光轴的光射到凹透镜上,其折射光线的反向沿长线会聚在虚焦点上。
5.主轴:
透镜上通过两个球心的直线叫做主光轴,简称主轴。
6.光心:
每个透镜主轴上都有一个特殊点:凡是通过该点的光,其传播方向不变,这个点叫做光心。
7.焦点:
凸透镜能使平行于主轴的光会聚在一点,这个点叫做凸透镜的实焦点,简称焦点。
凹透镜能使平行于主轴的光其折射光线的反向沿长线会聚在一点,这个点叫做凹透镜的虚焦点。
8.焦距:
焦点到光心的距离叫做焦距。
9.测量凸透镜焦距的方法:
拿一个凸透镜正对着阳光,再把一张纸放在它的另一侧,改变透镜与纸的距离,直到纸上的光斑变得最小、最亮。测出这个最小、最亮的光斑到凸透镜的距离,这个距离就是凸透镜的焦距。
 
 
二、生活中的透镜
1.照相机成像特点:倒立缩小的实像。
2.投影仪成像特点:倒立放大的实像。
3.放大镜成像特点:正立放大的虚像。
4.凸透镜成实像时,物和像在凸透镜两侧。
5.凸透镜成虚像时,物和像在凸透镜同侧。
 
三、凸透镜成像规律
1.凸透镜成像规律:


(1) 一倍焦距是成实物与虚像、倒正、物像异同侧的分界点。物距大于一倍焦距时,物体成实像(倒立,物像同侧);物距小于一倍焦距时,物体成虚像(正立、物像异侧);
(2) 二倍焦距是成像大小的分界点。物距大于二倍焦距时,物体成缩小的像;物距小于二倍焦距时,物体成放大的像;
(3)实像都是倒立的(物、像同侧),虚像都是正立的(物、像异侧);
  (没有缩小的虚像,也没有等大的虚像)
(4)成实像时,物近像远,像变大(物远像近,像变小);
成虚像时,物远像远,像变大(物近像近,像变小)。
 
 
四、眼睛和眼镜
67.眼睛:
1.眼睛通过睫状体来改变晶状体的形状。
2.看远处物体时,睫状体放松,晶状体变薄,对光的偏折能力变小,远处物体射来的光刚好聚在视网膜上,眼睛可以看清远处的物体;
3.看近处物体时,睫状体收缩,晶状体变厚,对光的偏折能力变大,近处物体射来的光刚好聚在视网膜上,眼睛可以看清近处的物体。
4.近视眼矫正:佩戴凹透镜。
5.远视眼矫正:佩戴凸透镜。
 
五、显微镜和望远镜
1.显微镜成像原理(虚像):
来自被观察物体的光经过物镜后成一个放大的像,道理就像投影仪的镜头成像一样;目镜的作用则像一个普通的放大镜,把这个像再放大一次。
2.望远镜成像原理:
物镜的作用是使远处的物体在焦点附近成实像,道理就像照相机的镜头成像一样;目镜的作用相当于一个放大镜,用来把这个像放大。
3.视角:
同一个物体,离眼睛近时,视角大,在视网膜上所成的像也大;离眼睛远时,视角小,在视网膜上所成的像也小;
 
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