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A photographer uses a camera lens with focal length of 50.0 mm to photograph a tree that is 4.60 m tall. She wishes to fill her 24.0-mm slide with the tree.

(a) How far from the lens should the film be?

(b) What is the magnification of the image?

Julius  Jan 15, 2018
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#1
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A couple of physics equations (again )

M= hi / ho = - di / do       (1)        and   f = 1/do + 1/di     (2)

Using (1)

M = 24 mm / 4600 mm = .005217  = magnification

also using (1)   di =- hi/ho * do = -  .005217 do       (we'll substitute this in to (2)  )

Using (2)

1/50 = 1/do + 1/di    Substitiute for di

1/50 = 1/do + 1 /(-.005217do)

1/50 = 1/do - 191.666/do         =   distance from object to lens

do = - 9533.33 mm      (negative means object side of the lens) = 9.533 m from the lens

(Hope I did the calcs correctly! )

ElectricPavlov  Jan 16, 2018
#2
+12248
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Sorry.....I gave the distance of the OBJECT from the lens....to find the distance of the FILM from the lens, it is very similar:

also using (1)   do =-di/ hi/ho  = - 191.666 di

1/50 = 1/(-191.666di) + 1/di

1/50 = .994783/di

di=49.73mm = distance from lens to film

ElectricPavlov  Jan 17, 2018

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