Optical Instruments34525.14(a) When the child clearly sees objects at her far point ( )max125 cmp=the lens-cornea combination has assumed a focal length suitable of forming the image on the retina ( )2.00 cmq=. The thin lens equation gives the optical power under these conditions as 111rs1.25 m0.020 0 min metersfpq==+=+50.8 diopte=+farPWhen the eye is focused ( )2.00 cmq=on objects at her near point ( )minp10.0 cm=the optical power of the lens-cornea combination is 1m0.020 0rin meters+10.100q+=160.0 diopm=+tersneaP(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 cmq=−. The optical power of the required lens is 108001.25in metersq+=+−−P10.m=diopters Since the power, and hence the focal length, of this lens is negative, it is
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