344CHAPTER 25 25.11His lens must form an upright, virtual image of a very distant object (p≈ ∞80.0 c) at his far point, 80.0 cm in front of the eye. Therefore, the focal length is mfq==−. If this lens is to form a virtual image at his near point (18.0qcm), the object distance must be ( )( )()18.0 cm80.0 cm23.2 cm18.0 cm80.0 cmqfpqf−−===−−25.12(a) The lens should form an upright, virtual image at the near point ( )100 cmqwhen the object distance is 25.0 cmp=. Therefore, ( )25.0 cmcm25.0 cmpqfpq−+−100 cm33.3100 cm=(b) The power is 113.00 diopters
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