Finding the Optimal Lens Position for a Sharp Image of a Candle

AI Thread Summary
To find the optimal lens position for a sharp image of a candle placed 1.8 m from a screen, the thin lens formula is applicable. The formula 1/f = 1/do + 1/di can be rearranged to determine the distance of the lens from the candle. By substituting the focal length of 0.21 m and the total distance of 1.8 m, the equation becomes 1/x + 1/(1.8 - x) = 1/0.21. Solving this equation will yield the correct position for the lens to achieve a sharp image on the screen. Understanding and applying this formula is crucial for success in the test.
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A candle is placed 1.8 m from a screen. whereshould a lens of focus length 21 cm (0.21 m) be placed between the screen and the candle to prduce a sharp image screen?

The only formula i could think of was 1/f=1/do+1/di



I've now spent 3 hours on this (test tomorrow) and still don't know where to start. I have that first formula and the only other formula we've used had to do with magnification and object height. I am truly lost.
 
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Welcome to PF.

Looks like the thin lens formula applies here doesn't it?

So ... won't the distance x be able to be found by

1/x + 1/(1.8 - x) = 1/.21 ?
 

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