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A equiconvex lens of focal length 30 cm ...

A equiconvex lens of focal length 30 cm is divided into two equal halves in thickness.find the focal lnegth of eah half.

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Focal length of the double convex lens `=f=+15cm`
Let `f_(1)=f_(2)=f.=` focal length of each half piece of the lens
We know `1/f=1/(f_(1))=1/(f_(2))`
`1/15=1/(f.)+1/(f.)=(1+1)/(f.)`
`1/15=2/(f_(1))`
so `f.=2xx15=30cm`
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