Ray Optics

JEE Main level, single correct, medium

184 of 295

Question 184 of 295

The refractive index of a converging lens is 1.41.4. What will be the focal length of this lens if it is placed in a medium of same refractive index ? (Assume the radii of curvature of the faces of lens are R1{R}_{1} and R2{R}_{2} respectively)

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Answer: (B) Infinite

1F=[μLμS−1][1R1−1R2]\dfrac{1}{F}=\left[\dfrac{{\mu }_{L}}{{\mu }_{S}}-1\right]\left[\dfrac{1}{{R}_{1}}-\dfrac{1}{{R}_{2}}\right]
If μL=μS⇒1F=0⇒F=∞{\mu }_{L}={\mu }_{S}\Rightarrow \dfrac{1}{F}=0\Rightarrow F=\infty

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