A stamp collector is viewing a stamp with a magnifying glass held next to her ey

Question

A stamp collector is viewing a stamp with a magnifying glass held next to her eye. Her near point is 25 cm from her eye. (a) What is the refractive power of a magnifying glass that has an angular magnification of 7.6 when the image of the stamp is located at the near point? (b) What is the angular magnification when the image of the stamp is 42 cm from the eye?

Explanation / Answer

The image is formed at 25 cm from lens Also it is given that magnification is 7.6 So magnification = image distance / object distance = v /u => v = 7.6 u Image distance v= - 25 cm so object distance u = v /6.52 = (-25 / 6.2) = - 4.03 cm So using the lens formula 1/v - 1/u = 1/f We know 1/ focal length = power So 1/f = -1/.0025m - (-1/.00403m) = 20.8 So power = 1/f (in meters) = 20.8 D, the answer for part a. For part b, we have m= 1 + 42cm/4.03cm = 11.42 So you have answers of: a) 20.8 Diopters b) 11.42 Hope that helps, let me know if you have any questions, good luck!

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