物理反射題目

物理反射題目

2010-01-18 2:12 am

[IMG]http://i903.photobucket.com/albums/ac235/y4205985/PHYSICS-2.jpg[/IMG]

CD is the mirror and XY is the door.

1.A pinhole video camera is now set at O.For the camera to film the whole door XY through the mirror CD hung on the opposite wall, what is the minimum length of the mirror CD?

2.If AB is the mirror, what is the minimum length of the mirror AB so that the camera can film the whole door XY?

更新1:

請自行移至圖片的網頁連結

更新2:

第一題正確答案為0.655m 第二題為1.5m please show the steps with simple explain.

回答 (1)

天同

2010-01-22 6:08 am

✔ 最佳答案

First draw the image of door XY formed by mirror CD (see diagram)

[IMG]http://i250.photobucket.com/albums/gg258/easygophoto/show2/diagram.jpg[/IMG]

On the diagram, X’ Y’ represents the image of XY, using similar triangles
C’F/Y’F = OR/Y’R
i.e. C’F/(3+1) = 4/(13+3+1)
hence, C’F = 4x4/17 m = 0.9412 m

D’F/X’F = OR/X’R
D’F /1 = 4/(13+1)
D’F = 4/14 m = 0.2857 m

Hence, length of mirror = C’F – D’F = 0.6555 m
Refer to the diagram, the image of X’Y’ on the mirror AB is represented by X”Y”
Again, by similar triangles
A’S/X”R’ = OS/OR’
A’S/(13+1) = 4/(8+4)
i.e. A’S = 14 x 4/12 = 4.6667 m

Since BS = (13-7) m = 6 m
Hence, length of mirror = (6-4.6667) m = 1.33 m

Please check whether your given answer is correct.

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物理 反射 題目

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