A bi-convex lens made of glass (refractive index ${\rm{1}}{\rm{.5}}$) is put in a liquid of refractive index ${\rm{1}}{\rm{.5}}$. Its focal length will

Decrease and remain of the same sign

Increase and remain of the same sign

JEE PHYSICS MCQ: RAY OPTICS

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Application +4 | -1

A bi-convex lens made of glass (refractive index

\mathrm{1}\mathrm{.5}

) is put in a liquid of refractive index

\mathrm{1}\mathrm{.5}

. Its focal length will

View answer and explanation

Correct option: B

Increase and change sign

Option B (Increase and change sign) is correct because when the lens is immersed in a medium with the same refractive index, its focal length becomes infinite and then changes sign as the refractive index of the liquid is slightly different.

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