Verified Solution • 2025–26 Session
moderate
QAIPMT-2003-Ph-2721: NEET 2003 Physics - Class 12 AIPMT-2003-Ph-2721 Solution: An equiconvex lens is cut into two halves along (i) XOX' and…
An equiconvex lens is cut into two halves along (i) XOX' and (ii) YOY' as shown in the figure. Let f, f', f'' be the focal lengths of the complete lens, of each half in case (i), and of each half in case (ii), respectively. Choose the correct statement from the following
Multiple Choice Options
- A
- B
- C
- D
Step-by-Step Verified Solution
We know from Lens maker's formula
1 f = ( _ _ 1 ) ( 1 R 1 _ 1 R 2 )
Initially, Here R 1 = R and R 2 = �R by convection.
_ 1 f = ( _ _ 1 ) 2 R
_ 1 2 f = ( _ _ 1 ) 1 R
If we cut the lens along XOX' then the two halves of the lens will be having the same radii of curvature and so, focal length f' = f .
But when we cut it along YOY' then, we will have
R 1 = R but R 2 = �
_ 1 f _ = ( _ _ 1 ) ( 1 R _ 1 � ) = ( _ _ 1 ) 1 R = 1 2 f
_ f'' = 2f