A stamp collector is viewing a stamp with amagnifying glass held next to her eye

Question

A stamp collector is viewing a stamp with amagnifying glass held next to her eye. Her near point is 25 cm fromher eye. (a) What is the refractive power of amagnifying glass that has an angular magnification of 4.0 when the image of the stamp is located at the nearpoint (b) What is the angular magnification when theimage of the stamp is 40 cm from theeye? A stamp collector is viewing a stamp with amagnifying glass held next to her eye. Her near point is 25 cm fromher eye. (a) What is the refractive power of amagnifying glass that has an angular magnification of 4.0 when the image of the stamp is located at the nearpoint (b) What is the angular magnification when theimage of the stamp is 40 cm from theeye? (a) What is the refractive power of amagnifying glass that has an angular magnification of 4.0 when the image of the stamp is located at the nearpoint (b) What is the angular magnification when theimage of the stamp is 40 cm from theeye?

Explanation / Answer

(a)
   from the given question with the image at the nearpoint of the eye the angular magnification will
   be
   M = (N / f) + 1
   from which we get
   (N / f) = M - 1
   f = N / (M - 1)
     = (25 cm) / (4.0 - 1)
     = ........ m
   now the refractive power of the lens will be
   RP = 1 / f
         = ......diopters
(b)
   when the image of the stamp is 45 cm from the eye
   M = [(1 / f) - (1 / di)] N
        = [(1 / f) - (1 / -0.40m)] (0.25 m)
        = .........

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