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如图所示,物理兴趣小组想知道某只透镜的焦距 f 为多少,做实验甲,镜面垂直于阳光,在透镜下面放上白纸(纸、镜平行),测出透镜与白纸间距s/ cm与对应的白纸被烤焦的时间 t/ min,绘出图线乙,则可判断该透镜的焦距f为
。将透镜及蜡烛、光屏置于光具座上,(如图丙)做成像实验,记录每次成实像的物距u,像距v。物像间距L(u+v),绘出图线丁(以f为长度单位),由图可知,要想成实像,蜡烛与光屏的间距应满足:L
(用f表示)。经“百度”发现,物理学中,有一个凸透镜成像的“新概念”:放大率
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3En%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmsup%3E%3Cmrow%3E%3Cmi%3EA%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmi%3E%27%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3Cmsup%3E%3Cmrow%3E%3Cmi%3EB%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmi%3E%27%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmsup%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmi%3EA%3C%2Fmi%3E%3Cmi%3EB%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmfrac%3E%3Cmrow%3E%3Cmi%3Ev%3C%2Fmi%3E%3C%2Fmrow%3E%3Cmrow%3E%3Cmi%3Eu%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmfrac%3E%3Cmo%3E%2C%3C%2Fmo%3E%3C%2Fmath%3E)
结合丙、丁两图,可知当物距
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Eu%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E1.5%3C%2Fmn%3E%3Cmi%3Ef%3C%2Fmi%3E%3C%2Fmath%3E)
时,
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3En%3C%2Fmi%3E%3C%2Fmath%3E)
=
。
![](http://tikupic.21cnjy.com/2024/12/09/86/1c/861c6eb8b1347d5013477b65e2a4686d_570x116.png)