Question

A lens of material of refractive index n2 is surrouded by a medium of refractive index n1 . The focal length 'f' is related as_____

Answer 1

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If a lens is surrounded by air,

It's focal length is calculated or is given by,

$= > \it \frac{1}{f} = (n - 1)( \frac{1}{ r_{1} } - \frac{1}{ r_{2}} )$
Where f = focal lenght;

=> n = refractive index of lens.

=> r1 and r2 are the radius of curvatures.

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If the lens has n2 and is surrounded by refractive index n1,

we can write focal length as,

$= > \bf \frac{1}{f} = ( \frac{n _{2} }{ n_ {1} } - 1)( \frac{1}{ r_{1} } - \frac{1}{ r_{2}} )$
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