JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
A planoconvex lens becomes an optical system of \(28\, cm\) 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 other side as in Fig. \(B\), it acts like an optical system of focal length \(10 \,cm\). The refractive index of the material of lens is
- A \(1.50\)
- B \(1.55\)
- C \(1.75\)
- D \(1.51\)
Answer & Solution
Correct Answer
(B) \(1.55\)
Step-by-step Solution
Detailed explanation
Effective focal length of the combination, \(\frac{1}{F}=\frac{2}{f}+\frac{1}{f_{m}}\) \(f_{m} \Longrightarrow \infty\) This gives, \(f=56\) \(f_{m}=\frac{R}{2}\) Hence, \(\frac{1}{F}=\frac{2}{f}+\frac{2}{R}\) This gives, \(R=31.11\)…
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