An arrow 2.0cm long is located 74.5cm from a lens that has a focal length f = -2

Question

An arrow 2.0cm long is located 74.5cm from a lens that has a focal length f = -28.5cm . (Figure 1)

A) If the arrow is perpendicular to the principal axis of the lens, as in the figure (a), what is its lateral magnification, defined as hi/ho? THE ANSWER IS 0.277

BUT I CANT FIGURE OUT B... PLEASE HELP. THANKS!

B) Suppose, instead, that the arrow lies along the principal axis, extending from 73.5cm to 75.5cm from the lens, as indicated in the figure (b). What is the longitudinal magnification of the arrow, defined as Li/Lo? (Hint: Use the thin-lens equation to locate the image of each end of the arrow.)

Explanation / Answer

1/S1 + 1/S1' = 1/F

(1/73.5) + (1/S1') = -1/28.5

S1' = ?20.53676 cm

1/S2 + 1/S2' = 1/F

(1/75.5) + (1/S1') = -1/28.5

S2' = ?20.6899 cm

S1' - S2' = 0.15314 cm

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