A stamp collector is viewing a stamp with a magnifying glass heldnext to her eye

Question

A stamp collector is viewing a stamp with a magnifying glass heldnext to her eye. Her near point is 25 cm from her eye.

(a) What is the refractive power of amagnifying glass that has an angular magnification of 8.0 when the image of the stamp is located at the nearpoint?
1 diopters

(b) What is the angular magnification when the image of the stampis 48 cm from the eye?
?????? (a) What is the refractive power of amagnifying glass that has an angular magnification of 8.0 when the image of the stamp is located at the nearpoint?
1 diopters

(b) What is the angular magnification when the image of the stampis 48 cm from the eye?
??????

Explanation / Answer

a) with the image at the near point of the eye , theangular magnification is M = N/f +1    from this we have f = N/(M-1)                                  = 25cm / (8.0-1)                                   = 3.571cm                                    = 0.0357m the refractive power of this lens is      refractive power = 1/f =1/0.0357m                                        = 28 diopters b) when the image of the stamp is  48 cm from the eye, then angular magnificationis      M = (1/f -1/di)*N           =[1/(0.0357m ) - 1/(-0.48m)]*0.25m          = 7.52

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