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NEET · Physics · STD 12 - 9. Ray optics and optical instruments
Two similar thin equi-convex lenses, of focallength feach, are kept coaxially in contact with each other such that the focallength of the combination is \(\mathrm{F}_{1}\). When the space between the two lenses is filled with gyoern(which has the same refractive index ( \(\mu =1.5\) ) as that of glass then the equivalent focal length is \(\mathrm{F}_{2} .\) The ratio \(\mathrm{F}_{1}: \mathrm{F}_{2}\) will be
- A \(2:1\)
- B \(1:2\)
- C \(2:3\)
- D \(3:4\)
Answer & Solution
Correct Answer
(B) \(1:2\)
Step-by-step Solution
Detailed explanation
\(\frac{1}{\mathrm{F}_{1}}=\frac{1}{\mathrm{f}}+\frac{1}{\mathrm{f}}\) \(\Rightarrow \mathrm{F}_{1}=\mathrm{f} / 2\)
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