346CHAPTER 25 (b) The lower part of the lens should form an upright, virtual image at the near point of the eye ( )30 cmq=−when the object distance is 25 cmp=. From the thin lens equation, ()( )230 cm1.510 cm30 cmf−=+×+−25 cm25 cmpqpq==1.5 m=+Therefore, the power is 110.671.5 mf=++Pdiopters 25.17(a) The simple magnifier (a converging lens) is to form an upright, virtual image located 25 cm in front of the lens ( )25 cmq. The thin lens equation then gives ( )( )25 cm7.5 cm25 cm7.5 cmqfpqf−−− −5.8 cm=+so the stamp should be placed 5.8 cm in front of the lens
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