An insect 3.90 mm tall is placed 22.7 cm to the left of a thin planoconvex lens.

Question

An insect 3.90 mm tall is placed 22.7 cm to the left of a thin planoconvex lens. The left surface of this lens is flat, the right surface has a radius of curvature of magnitude 12.7 cm, and the index of refraction of the lens material is 1.75.

(a) Calculate the location of the image this lens forms of the insect.

Calculate the size of the image.
mm??

(b) Repeat part (a) if the lens is reversed.
Calculate the location of the image this lens forms of the insect.

Calculate the size of the image.
mm?

Explanation / Answer

a) 1/f = (n - 1 ) ( 1/R1 - 1/R2)

     = (1.75 - 1) ( 1/infinity - 1 /-12.7)

f = 16.93 cm

Now using lens equation,

1 /22.7   + 1/i   = 1/16.93

i = 66.61 cm

m = -i/o = hi / ho

66.61 / 22.7 = hi / 3.90

hi = 11.44 mm

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