2.2 光的直线传播 2024-2025学年苏科版八年级上册物理

课题名称

八年级物理上册

2.2 光的直线传播

学习目标

1、能通过探究，归纳得出光的传播规律，进而能用光的直线传播来理解小孔成像，日食月食等现象。

2、了解光的传播需要一定的时间，知道真空中、空气中的光速。

3、了解我国古代在光现象研究上的成就，知道中华文明对科学发展做出的贡献                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

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 我们能看到周围的物体，是因为有来自物体的光进入了我们的眼睛。经验告诉我们，光可以在空气、水和玻璃中传播。那么，光的传播路径是怎样的？

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活动一：观察光的传播路径

1、自主思考：（1）猜一猜光在空气中的传播路径是怎样的？你有什么生活经验支持你的猜想？

           （2）如何显示光的传播路径？

2、自主观察：教师演示光空气、水等透明介质中的的传播路径。

3、小结：光在_____________中沿_____传播。

4、自主阅读：课本P42，认识光线，完成以下填空：

（1）我们用一条带有_______的_______表示光传播的路径和方向，称为光线。

（2）光线是人们为了研究光而引入的物理_____,实际上并不存在。

（3）当烛焰、灯泡离我们较远时，可以将其看成_____光源；在地面接收到的太阳光，可看成_______光。

活动二：利用光的直线传播原理解释现象

1、小组交流：利用光的直线传播原理解释现象：

（1）影子：由于光沿_______传播,不能绕过物体进行传播，在不透明物体的后方会有光________的区域，便形成影子。

（2）日食：______处在______和太阳之间，由于光沿_______传播，挡住了太阳射向_______的光；月食：______处在______和太阳之间，由于光沿_______传播，挡住了太阳射向_______的光。

（3）小孔成像：由于光沿_______传播，成的是____的_____像；像的形状和_____形状一样；孔的大小和形状_______像的形状；物体______小孔，或光屏______小孔，像会变大。

活动三：了解光速

1、自主思考：打开电灯，灯光立即照亮整个房间，是否说明光的传播不需要时间？为什么？

2、信息快递：（1）光在真空中的传播速度是______________。光在空气中的速度非常接近于真空中的速度，光在水中的速度约为真空中速度的 3/4，在玻璃中的速度约为真空中速度的 2/3 。

（2）宇宙中恒星间的距离都非常大。为了表达起来方便一些，天文学家使用一个非常大的距离单位

——光年，它等于光在真空中传播1年经过的的距离。所以光年是_______单位。

3、自主阅读：课本P61“生活物理社会”。

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一、光的直线传播

1、2020年6月21日，我国的大部分地区观测到了日环食奇观，如图，日食的形成主要是由于（　　）

A、光的直线传播     B、小孔成像    C、平面镜成像     D、光的折射

2、2020年6月21日，我国的大部分地区观测到了日环食奇观，如图，发生这种天文现象时，太阳、地球和月亮的位置关系是（　　）

A、太阳--月亮--地球     B、地球--太阳--月亮  

C、月亮--太阳--地球     D、太阳--地球--月亮

3、2004年6月8日下午在我国发生了“金星凌日”的天文奇观。“金星凌日”是在地球上看到金星从太阳面上移过的现象，它的产生和日食的道理相同。如图为发生“金星凌日”现象时的示意图，图中金星的位置在（　　）

A、甲  B、乙   C、丙    D、丁

4、“举杯邀明月，对影成三人”，其中的“影”，它是由光的_____________形成的。

5、下列现象由光沿直线传播形成的是（                ）

A、人在地上的影子     B、手在墙上的影子    C、皮影戏荧幕上的人物

D、树在湖面的倒影     E、日食      F、月食    G、节食      H、小孔成像

6、假如光在同一均匀介质中不沿直线传播，下列现象可能出现的是（　　）

A、做操时更容易将队伍排直      B、地球上没有昼夜之分

C、阳光下的人影更清晰          D、更容易形成日食和月食

7、皮影戏”是我国的民间艺术，演员只要在屏幕和灯光之间抖动拴在道具“小兔”身上的细线，屏幕上就能出现生动活泼的小兔形象。这其中所涉及的光学知识主要是__________________。如果将“小兔”靠近灯光，那么屏幕上小兔的影子将__________（填“变大”、“变小”或“不变”）。

8、小东与几位同学做手影游戏时发现，手影大小经常在改变，影子的大小与哪些因素有关？他猜想：影子的大小可能与光源到物体的距离有关，他们借助如图甲所示的实验装置，来探究影子高度与光源到物体距离的关系。实验中，把手电筒正对黑板擦由近及远先后放在距离黑板擦不同位置，保持其他因素不变，分别测量影子在墙面上的高度。记录数据如表：

（1）分析数据他们发现：若保持其他因素不变，当手电筒由近处逐渐远离黑板擦时，影子的高度随之______________。

（2）为了进一步发现其中的规律，他们根据数据绘制了影子高度H随手电筒到黑板擦距离L变化的图象（图乙）。由图象可知，当手电筒到黑板擦的距离L=35cm时，影子的高度H大致是_________cm。

（3）当手电筒距黑板擦较远时，观察图象的变化趋势发现，影子变小得_______（填“快”或“慢”）；

当手电筒距离黑板擦足够远时，影子大小将__________________（填“逐渐变大”、“逐渐变小”或“基本不变”）。

二、小孔成像

1、如图所示，小明想通过A、B两张纸片上的小孔看见烛焰，他应将烛焰、两个小孔和人眼调到 ________________，这样操作的依据是______________________原理，操作过程中他还在B（半透明）纸片上看到了一个烛焰的像，这个像是________（选填“正立”或“倒立”）的，如果只改变A纸片上孔的形状，则B纸片上的像形状_______（选填“改变”或“不变”）。

2、同学们在课下的实践中是否做过这样一个实验在纸上剪一个很小的“▽”形孔，让太阳垂直照射到“▽”形孔上，去观察地面上的光斑？那么地面上形成的光斑是（　　）

A、“▽”形  B、“Δ”形  C、圆形     D、无法判定

3、如图所示，用自制的针孔照相机观察烛焰，有以下四种说法，其中不正确的有（　　）

A、薄膜上出现的像是倒立的

B、薄膜上的像可能是缩小的也可能是放大的

C、保持小孔和烛焰的距离不变，向后拉动薄膜，烛焰的像更明亮

D、保持小孔和烛焰的距离不变，向前推动薄膜，烛焰的像变小

4、如图所示将点燃的蜡烛置于自制的小孔成像仪前，调节二者的位置，在屏上得到如图所示的蜡烛清晰倒立的像：

（1）该现象可以用__________________来解释；

（2）请在图中确定成像仪上小孔O的位置（保留作图痕迹）。

（3）实验过程中蜡烛燃烧不断缩短，导致光屏上的像向_______（选填“上”或“下”）方移动；若将蜡烛靠近成像仪少许，蜡烛的像将_______（选填“变大”、“变小”或“不变”）。

（4）若只将小圆孔改为三角形小孔，则像的形状_______（选填“改变”或“不变”）。

6、小明通过阅读课本了解到小孔会成上下颠倒，左右相反的像，为了验证这个说法，他准备制作一个LED屏作为物体进行研究，下列关于LED屏制作形状的选择最适合的是（　　）

7、2009年夏季，中国出现了日食奇观。小华借助小孔成像实验装置对“   ”形太阳进行观