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QNEET-2016-Ph-1169: NEET 2016 Physics - Class 12 NEET-2016-Ph-1169 Solution: Two identical glass (\( _g = 3/2\)) equiconvex lenses of focal…
Two identical glass () equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water (). The focal length of the combination is f/3 f 4f/3 3f/4
Multiple Choice Options
- A f /3
- B f
- C 4 f /3
- D 3 f /4
Step-by-Step Verified Solution
Focal length (f) of glass convex lens is given by
1 f = ( _ g _ 1 ) ( 2 R )
_ 1 f = ( 3 2 _ 1 ) ( 2 R )
_ f = R
Focal length (f 1 ) of water filled concave lens is given by
1 f 1 = ( _ w _ 1 ) ( _ 2 R )
_ 1 f 1 = ( 4 3 _ 1 ) ( _ 2 R ) = _ 2 3 R = _ 2 3 f
Equivalent focal length (f eq ) of lens system
1 f e q = 1 f _ 2 3 f + 1 f = 4 3 f
_ f eq = 3 f 4