if a covex lens is cut horizontally from the middle what will happen to its focal length?also consider the case of a concave lens.

If a convex lens is cut horizontally from optical axis i.e., from middle, then radii of curvature on both sides of the lens i.e., R1 and R2 will remain same as before.
As focal length is given by formula :-
1f = μ -11R1-1R2  ( By Lens Maker formula )
As R1 and R2 do not change, so there will be no change in focal length of the lens.

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1/focal length of full lens=1/focal lengh of half lens cut from verticle+1/focal length of other half lens cut from verticle

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still didnt get the answer.... and i cut the lense half by a horizontal plane from the middle and not by a vertical one... nd its vertical not verticle.... :)

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1/f = (n-1)(1/R1 +1/R2) =(n-1)2/R -------- 1 (since it is biconvex lens )

when it is cut into to halves

1/f1 = (n-1) 1/R -----------2

dividing 1 and 2 we get

f1/f = 2

f1 = 2f

this shows that the new focal length will be 2 times the original focal lenght .

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i am not talking about biconvex ...

i am saying that if one portion of the lens (either above or below )is cut from the optical axis... what will happen to its focal length..?.

pls see the below diagram... it represents the convex lens cut from the optical axis!!!

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sry image is not being displayed.. and i am able to send u the site also... :P..

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hy i got the answer guys if we cut the cut convex lens either from above or below from the optical axis the INTENSITY will change... and hence the focal length remains same....cheers..:)

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