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Homework Statement
Two 28.0-cm-focal-length converging lenses are placed 16.5 cm apart. An object is placed 36.0 cm in front of one lens. Where will the final image be formed by the second lens?
Homework Equations
1/do + 1/di = 1/f
The Attempt at a Solution
for the first lens:
1/do + 1/di = 1/f
1/di =1/28 - 1/36 = 8/1000
di = 125cm
This is where I get confused I used 125cm as my do2 but the solution tells me I have to do 16.5cm - 125cm. My question is since the image due to lens 1 is 125cm away from lens 1, why would i have to subtract the lens separation in order to get do2? I know that do2 is a negative number but not why i have to take into account the lens seperation.
Thanks for you help