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9_Chapter 25 HomeworkCH25 Optical Instruments

# 9_Chapter 25 HomeworkCH25 Optical Instruments - Optical...

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Optical Instruments 345 25.14 (a) When the child clearly sees objects at her far point ( ) max 125 cm p = the lens-cornea combination has assumed a focal length suitable of forming the image on the retina ( ) 2.00 cm q = . The thin lens equation gives the optical power under these conditions as 11 1 rs 1.25 m 0.020 0 m in meters fp q == + =+ 50.8 diopte = + far P When the eye is focused ( ) 2.00 cm q = on objects at her near point ( ) min p 10.0 cm = the optical power of the lens-cornea combination is 1 m 0.020 0 r in meters + 1 0.100 q + = 1 60.0 diop m = + ters nea P (b) If the child is to see very distant objects ( ) p →∞ clearly, her eyeglass lens must form an erect virtual image at the far point of her eye ( ) 125 cm q =− . The optical power of the required lens is 1 0 800 1.25 in meters q + = + P 1 0. m = diopters Since the power, and hence the focal length, of this lens is negative, it is
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