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Optics Question: Power of Focal Length

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a) The far point of an eye is 75cm in front of the the eye. What power of focal length should the prescribed spectacles be in order for the eye to distinctly see a distant object?

b) With these spectacles, the near point is 25cm in front of the eye; where would it be without them?

c) A person with normal vision (near point 25cm) puts on the spectacles. Over what range is he able to see objects clearly? Over what range are the images formed by the spectacles for the range of the clearly seen objects to just be determined?

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Solution Summary

The power of focal length are determined.

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Here is the solution :

(a)

The far point is 75 cm which must be at infinity. This means that the spectacle lens must make the rays coming from infinity appear to come from distance of 75 cm.

1/v - 1/u = ...

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