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Old Jan 24th 2009, 09:49 PM   #1
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Join Date: Jan 2009
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Focal Length...

Got some work from my dad, but one question kinda stumped me.

A short sighted person can view an object clearly only when it is between 11 cm and 19 cm from her eyes. Calculate:
1. The Focal Length of the specatacles required to give her a near point of 25 cm.

I don't know what equation to use here. I usually see questions about image and object distances and object distances using the 1/u+ 1/v= 1/f equation, I've never seen one like this. Can anyone help me out here?
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