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NEET 2019
Exam
NEET
Year
2019
Subject
Physics
Chapter
Ray Optics

NEET 2019 · Physics · Ray Optics

Two similar thin equi-convex lenses of focal length f each are kept...

Two similar thin equi-convex lenses of focal length ff each are kept coaxially in contact with each other, such that the focal length of the combination is F1.{F}_{1} . When the space between the two lenses is filled with glycerin (which has the same refractive index (μ=1.5\mu = 1.5) as that of glass), then the equivalent focal length is F2.{F}_{2} . The ratio F1:F2{F}_{1}: {F}_{2} will beTwo similar thin equi-convex lenses of focal length f each are kept coaxially in contact with each other, such that theTwo similar thin equi-convex lenses of focal length f each are kept coaxially in contact with each other, such that the

Options

  1. A2:12: 1
  2. B1:21: 2
  3. C2:32: 3
  4. D3:43: 4

Correct answer

B. 1:21: 2

Step-by-step solution

Case I:
Two similar thin equi-convex lenses of focal length f each are kept coaxially in contact with each other, such that the
1Feq+1F+1F\dfrac{1}{{F}_{eq}} + \dfrac{1}{F} + \dfrac{1}{F}
F1=Feq=F2{F}_{1} = {F}_{eq} = \dfrac{F}{2}
Case II:
Two similar thin equi-convex lenses of focal length f each are kept coaxially in contact with each other, such that the
F2=Feq=F{F}_{2} = {F}_{eq} = F
F1:F2=1:2{F}_{1}: {F}_{2} = 1: 2
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