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# [問題] Phy mc一問 (light wave)

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## Phy mc一問 (light wave)

1974ce

A parallel beam of rays after passing through a converging lens L converges to a point F. If the lens is now completely surrounded by a clear liquid having the same refractive index as the lens, you would expect the beam to
A. converge to the point X
B. converge to the point F
c. converge to the point Y
d. emerge as a parallel beam
ANS:C

AL1981#19
The image of an object formed on a screen by a thin converging lens has a height a. By moving the lens towards the screen, a second lens position is found at which the height of the image formed on the screen is b. What is the height of the object?
a. 1/2(a+b)
b. 1/2(ab)^(1/2)
c.(ab)^(1/2)
d.(a^3/b)^(1/2)
ANS: C

[ 本帖最後由 karacyyu 於 2012-8-2 05:54 PM 編輯 ]

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## 回覆 1# karacyyu 的帖子

1.  無圖無真相

2. 設第1次的 lens-to-object distance 做x  ，lens-to-screen distance 做y
object 的高做M

y / x = b / M

2式兩相乘，易得︰M=(ab)^0.5

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