A 6.47-mm-high firefly sits on the axis of, and 11.7 cm in front of, the thin le

Question

A 6.47-mm-high firefly sits on the axis of, and 11.7 cm in front of, the thin lens A, whose focal length is 6.27 cm. Behind lens A there is another thin lens, lens B, with focal length 24.1 cm. The two lenses share a common axis and are 58.5 cm apart Is the image of the firefly that lens B forms real or virtual? O Virtual Real How far from lens B is this image located (expressed as a positive number)? Number cm What is the height of this image (as a positive number)? Number Is this image upright or inverted with respect to the firefly? O Upright O Inverted

Explanation / Answer

for lens A

object distance S1 = 11.7 cm

focal length f1 = 6.37 cm

image distance s1' = ?

1/s1 + 1/s1' = 1/f1

1/11.7 + 1/s1' = 1/6.37

s1' = 14 cm

magnification of lensA mA = -s1'/s1

mA = -14/11.7 = -1.19

for lens B

object distance s2 = 58.5 - 14 = 44.5 cm

focal length f2 = 24.1 cm

image distance s2' = ?

1/s2 + 1/s2' = 1/f2

1/44.5 + 1/s2' = 1/24.1

s2' = 52.6 cm

magnification of lens B mB = -s2'/s2 = -52.6/44.5 = -1.18

s2' is positive

IMage is Real

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image distance s2' = 52.6 cm

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hi/ho = mA*mB

hi/6.47 = 1.19*1.18

hi = 9.08 mm

==========================

Upright

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