can u plz tell me the relation b/w focal length and refractive index..
relation(formula)and its derivation.
on its basis solve numerical attached below:
a convergent lens is placed inside a cell filled with water .lens has focal length +20cm when it is in air ,and its material has refractive index 1.50.If the liquid has refractive index1.60 focal length of lens in cellis________cm.
1/f = ( n-1) ( 1/R1-1/R2) where r1 & r2 are the radii of the surfaces of the given lens
for derivation refer any state board text book
1/f1 ng - 1
--------- = ----------
1/f2 ng
----- - 1
nl
since refractive index of the liquid is more than the glass the con vex lens behaves as a concave lens . on substitution f2 = 160cm
Moderation Team
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