f .6 optical instrument

2011-03-09 1:54 am

1A person can see clearly objects at distances between 20cm and 200c, f4rom his eye.
(a0 what kings of lenses are required to enable him to see distant object clearly?
(b) What will be his least distance of distinct vision when he is wearing them?
2.An elderly person cannot see clearly, without the use of spectacles objects nearer than 200cm .
(a) What spectacle s will he need to reduce this distance to 25 com?
(B) If his eyes can focus rays which are converging to points not less than 1520 cm behind them, calculate his range of distinct vision when using the spectacle.

回答 (1)

天同

2011-03-09 5:59 am

✔ 最佳答案

1(a) Divergent lens with focal length 200 cm.
(b) 1/u + 1/(-20) = 1/(-200)
u = 22.2 cm
The least distance of distinct vision is 22.2 cm

2.(a) Converging lens.
1/25 + 1/(-200) = 1/f
f = 28.6 cm
The focal length of the converging lens is 28.6 cm

(b) JUst check your figure, 1520 cm is 15.2 m, which is much longer than the dimension of eye ball.

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