F.6 Optical instrument

2011-03-09 2:03 am

1.A person can focus objects only when they lie between 50 cm and 300 cm from his eyes.What spectacles should he use
(a) to increase his maximum distance of distinct vision to infinity ??
(b) to reduce his least distance of distinct vision to 25 cm?
In each case, find his new range of distinct vision.
02.. A man uses a converging lens of focal lengthj 50cm to correct his near points to 25 cm.he uses a diverging lens of focal length 200 cm to correct his far point to infinity .Find the range of distinct vision with his unaided eyes.

回答 (1)

天同

2011-03-09 5:44 am

✔ 最佳答案

1.(a) Diverging lens.
1/u + 1/(-50) = 1/(-300)
u = 60 cm
Hence, new range of distinct vision is from 60 cm to infinity.

(b) Converging lens
1/(-50) + 1/25 = 1/f
f = 50 cm
The spectacles should be of focal length 50 cm
For the max distance of distinct vision,
1/u +1/(-300) = 1/50
u = 43 cm
The new range of distict vision is from 25 cm to 43 cm
2. For the converging lens,
1/ 50 = 1/25 + 1/v
v = -50 cm

For the diverging lens,
1/infinity + 1/v = 1(-200)
v = -200 cm
Range of distinct vision is from 50 cm to 200 cm

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