Two identical glass μ g = 3 2 equiconvex lenses of focal length, f are kept in contact. The space between…

Two identical glass μg=32 equiconvex lenses of focal length, f are kept in contact. The space between the two lenses is filled with water μw=43. The focal length of the combination is
  1. f3
  2. f
  3. 4f3
  4. 3f4

Solution

1f=μg-12R=1R, μg=32R=f

1f1=-μw-12R=-23R=-23f.

1feq=1f+1f+1f1=1R+1R-23R

1feq=1f+1f-23f

1feq=2f-23f
1feq=43f
feq=3f4.

Asked in: NEET 2016 (Phase 2)

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