a student focussed the image of a candle frame on a white screen using a convex lens.He noted down the positions of the candle flame, screen and the lens as given below: (a)Position of candle flame=12 cm (b)Position of the screen=50 cm (c)Position of the screen=88 cm (i)find the focal length of the convex lens. (ii)find the position of the image of the candle flame if it is shifted towards the lens at a position of 31 cm (iii)State the nature of the image formed if the candle flame is further shifted towards the lens.

Asked by  | 28th Mar, 2013, 07:27: PM

Expert Answer:

(i)one info in the question is wrong:
b)Position of the screen=50 cm
it sh be:
b)Position of the lens=50 cm
so object distance=50-12=38 cm
image distance=88-50=38 cm
as the object distance and the image distamnce is equal so that means that the object is at 2f distance:
2f=38cm
f=19 cm
 
(ii)now the object distance=50-31=19 cm...so object at fous so the image will be at infinity
 
(iii)in this third condition virtual image will be formed.

Answered by  | 29th Mar, 2013, 02:12: PM

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