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Old Jul 6th 2009, 02:50 AM   #1
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Short sightedness and correction

A man can see clearly only objects which lie between 0.50m and 0.18m from his eye.
1) what is the power of the lens which when placed close to the eye would enable him to see distant objects clearly?
2) Calculate his least distance of distinct vision when using this lens.
for 1) object distance, u, would be 0.5 and image distance, v, would be -0.18? the answer is supposed to be -2D, where D is the least distance of distinct vision (i think)
for 2) i'm lost
thanks
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Old Jul 6th 2009, 06:30 PM   #2
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Originally Posted by arze View Post
A man can see clearly only objects which lie between 0.50m and 0.18m from his eye.
1) what is the power of the lens which when placed close to the eye would enable him to see distant objects clearly?
2) Calculate his least distance of distinct vision when using this lens.
for 1) object distance, u, would be 0.5 and image distance, v, would be -0.18? the answer is supposed to be -2D, where D is the least distance of distinct vision (i think)
for 2) i'm lost
thanks
In the first case , the corrective lens of focal length f should form an image at -0.5 m when the object is at infinity. That gives you the power -2D.
In the second case, find the image distance when the object is placed at 25 cm. If the image distance is more than 0.18 m he can see the object clearly. If it is less than 0.18m he cannot see the object clearly. His near point shifts closer.
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