Question

 (a) A 2.40-cm-high insect is 1.30 m from a 135-mm focal-length lens. Where is the image, how high is it, and what type is it? (b) What if f = -135 mm?

Answer 1

a)

$f=\frac{dF}{d-F}=\frac{1.3\cdot 0.135}{1.3-0.135}=0.15~m,$

$\Gamma=\frac fd=\frac{0.15}{1.3}=0.12.$

Image real, inverted, not magnified.

b)

$f=\frac{d|F|}{d+|F|}=\frac{1.3\cdot 0.135}{1.3+0.135}=0.12~m,$

$\Gamma=\frac fd=\frac{0.12}{1.3}=0.09.$

Image virtual, erect, not magnified.