# Answer to Question #25649 in Optics for dellu

Question #25649

if focal length of convex lens is f and it is cut into two equal part what is focal length of each part?

Expert's answer

There can be two ways to cut a convex lens into two equal parts - one, along the principal axis and another, perpendicular to the principal axis. If the lens is cut along the principal axis, then there will be NO change in the focal length of the lens. But, if it is cut perpendicular to the principal axis, then the focal length will be twice the original one.

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## Comments

Assignment Expert17.07.14, 17:38Dear Fatima,

The focal distance

fof a lens can be calculated using a lensmaker's equation:1/f = (n - 1)(1/R_1-1/R_2),where

nis a refractive index,R_1andR_2are curvature radii. For a biconvex lens theR_2is taken negative. If|R_1| = |R_2| = R, we havef = R/(2*(n-1)).If one cuts lens perpendicularly to the principal axis, the obtained lens will be convex only on the one side and flat on another side:

R_1 = RandR_2 = infinity. So,1/f_1= (n-1)/R =>f_1=R/(n-1)=2f.fatima19.06.14, 10:28explain plz??

infact i want to know is there any relation between diameter and focal length?

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