Case-1
f11=R(μ−1),f=−28⇒P=2p1+p2
⇒281=2(Rμ−1)
Case-2
f11=R(μ−1),f2=2R,f=−10cm
⇒P=2P1+P2⇒101=2(2μ−1)+R2⇒101=282+R2
R2=101−282=28018⇒R=9280cm⇒281=2(280μ−1)9
μ−1=95⇒μ=1+95=914=1.55.
JEE Main 2018 — Physics Optics
2018mcqhard
A plano-convex lens becomes an optical system of 28cm focal length when its plane surface is silvered and illuminated from left to right as shown in fig−A If the same lens is instead silvered on the curved surface and illuminated from another side as in fig-B, it acts as an optical system of focal length 10cm. The refractive index of the material of the lens is:
Official previous-year question
Held on 15 Apr 2018 · Verified 6 Jul 2026.
Options
- A
1.55
- B
1.50
- C
1.75
- D
1.51
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