Question

Please, explain

You are taking a photo of a poster on the wall of your dorm room, so you can't back away any farther than 3.2 m to take the shot. The poster is 0.70 m wide and 1.05 m tall, and you want the image to fit in the 15-mm x 22-mm frame of the film in your camera. Part A What is the longest focal length lens that will work? Express your answer using two significant figures. 10 AZN O O ?

Answer 1

Given object distance,

o= 3,2m

While taking a photo, image formed is inverted, so put negative sign

Image height,

h; = -22mm = -0.022m

Object height,

ho = 1.05m

Magnification,

Mhe

$\frac{h_{i}}{h_{o}}=-\frac{i}{o}$

-0.022m 1.05m 3.2m

0.022 1.05 39

0.022*3.2 1.05

i = 0,06705m

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Use formula

- oi

$\frac{1}{f}=\frac{1}{3.2m}+\frac{1}{0.06705m}$

$\frac{1}{f}=\frac{1}{3.2}+\frac{1}{0.06705}=\frac{0.06705+3.2}{3.2*0.06705}=\frac{3.26705}{3.2*0.06705}$

$f=\frac{3.2*0.06705}{3.26705}$

f = 0.065674m

ANSWER:
f = 6.5674cm

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