Help Solve Lens Projector Distance Puzzle!

AI Thread Summary
To determine the distance from the lens to the transparency for a slide projector using a converging lens with a focal length of 25 cm, the calculation involves the lens formula: 1/f = 1/s + 1/v. Given that the image distance (v) is 10m (or 1000 cm), the user calculated the object distance (s) as 25.64 cm. However, there is confusion regarding another value of 3.9 mm mentioned by another user, leading to uncertainty about the correct distance. Clarification on the source of the 3.9 mm value is requested, indicating a need for further discussion on the calculations.
cuddlylover
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I have this in my home work and i am not 100% on if i have it right or not

A converging lens with a focal length of 25 cm is used to make a slide projector. If the image is to be projected onto a screen 10m away, how far should the lens be located from the transparency?

I did it like this:

1/s + 1/1000cm = 1/25cm

solve for s

1/s = 1/25cm - 1/1000cm
∴ s = 25.64cm (2dp)

Is this right or am i way off. If some one could help would be a big help thanks.
 
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Or should it be 3.9mm i am a bit lost here i think lol.
 
Looks OK to me.
 
cuddlylover said:
Or should it be 3.9mm i am a bit lost here i think lol.
Where did you get that value?
 
I posted this somewhere else and someone posted that but could not see how they got to it :)
 

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