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[Phy] 1992-ce-phy I-3

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1992-ce-phy I-3

3.

Figure 4

A student holds a magnifying glass close to his eye to look at somesmall print on a paper. The image of the letters "EX" is shown inFigure 4. The magnification is 3.
(a)
Whatkind of lens is used as a magnifying glass ?

(1 mark)

Convex lens

(b)
Statethe nature (real or virtual, erect or inverted) of the image.

(2 marks)

The image is virtual and erect.
(c)
Thepaper is placed at a distance of 8 cmfrom the lens. In Figure 5, AB represents the object, and p, q are incidentrays. A scale of 1 cmrepresenting 4 cm for theobject distance is used.


(i)
Drawthe refracted rays of p and g and the image of AB in Figure 5.

+
(ii)
Fromthe ray diagram, measure


(1)
theimage distance,

16cm

(2)
the focal length of the lens.

Form lens formula:
1/u+1/v=1/f

(6 marks)

If you attempt Question 3, fill in the details in the first three boxesabove and tie this sheet into your answer book.

Figure 5


(d)
Ifthe paper is placed closer to the lens, how would the size of the image and theimage distance be affected ? Illustrate your answer with a ray diagram.

(4 marks)


(e)
Ifthe paper is moved away from the lens to a position beyond the focus, thestudent finds that a clear image cannot be observed. Explain briefly.

(2 marks)



[ 本帖最後由 stuzeus 於 2010-12-27 05:11 PM 編輯 ]
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冇講咩LENS

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convex

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無part(a)(b)好難答你。。

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ok已改

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since the magnification is 3, draw the image first (since it is virtual, draw it with dotted line and on the same side of the object) with image distance 24cm

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