Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main 202524 JanuaryMorning Shift
Exam
JEE Main
Year
2025
Date
24 January
Shift
Morning Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2025 · 24 January · Morning Shift · Physics · Ray Optics

A plano-convex lens having radius of curvature of first surface 2...

A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of f1f_1 in air. Another plano-convex lens with first surface radius of curvature 3 cm has focal length of f2\mathrm{f}_2 when it is immersed in a liquid of refractive index 1.2 . If both the lenses are made of same glass of refractive index 1.5 , the ratio of f1f_1 and f2f_2 will beA plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of f_1 in air. AnotherA plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of f_1 in air. Another

Options

  1. A1:21: 2
  2. B1:31: 3
  3. C3:53: 5
  4. D2:32: 3

Correct answer

B. 1:31: 3

Step-by-step solution

For case (1) A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of f_1 in air. Another
1.5v1−1∝=(1.5−1)R11f1−1.5v1=1−1.5∝\begin{aligned} & \frac{1.5}{v_1}-\frac{1}{\propto}=\frac{(1.5-1)}{R_1} \\ & \frac{1}{f_1}-\frac{1.5}{v_1}=\frac{1-1.5}{\propto}\end{aligned}\Rightarrow \frac{1}{f_1}=\frac{(1.5-1)}{R_1}...(1)...(1)\Rightarrow \frac{1}{f_1}=\frac{1}{2 R_1}Forcase(2)For case (2)1.5v1−1.2∞=(1.5−1.2)R21.2f2−1.5v1=(1.2−1.5)∝⇒1.2f2=0.3R2⇒1f2=14R2\begin{aligned} & \frac{1.5}{v_1}-\frac{1.2}{\infty}=\frac{(1.5-1.2)}{R_2} \\ & \frac{1.2}{f_2}-\frac{1.5}{v_1}=\frac{(1.2-1.5)}{\propto} \\ & \Rightarrow \frac{1.2}{f_2}=\frac{0.3}{R_2} \\ & \Rightarrow \frac{1}{f_2}=\frac{1}{4 R_2} \end{aligned}Soclearly,So clearly,\frac{f_1}{f_2}=\frac{2 \times 2}{4 \times 3}=\frac{1}{3}$A plano-convex lens having radius of curvature of first surface 2 cm exhibits focal length of f_1 in air. Another
Practice Ray Optics on Quantrex Academy →

More from Ray Optics

A double convex lens made of glass of refractive index 1.5 and radii of curvature of the… JEE Advanced 2026A beam of polychromatic light passes through a thin prism of prism angle 6^∘ . The… JEE Advanced 2026Consider two isosceles prisms 1 and 2 with prism angles A_1 and A_2 and refractive… JEE Advanced 2026A thin biconvex lens is prepared from the glass ( μ=1.5 ) both curved surfaces of which… JEE Main 2026Light ray incident along a vector AO ( AO = 2 i -3 j ) emerges out along vector OB ( OB =… JEE Main 2026Angle of minimum deviation is equal to the half of the angle of prism in an equilateral… JEE Main 2026A concave mirror of focal length 10 cm forms an image which is double the size of object… JEE Main 2026A spherical interface lens of radius R separates two media of refractive indices 1 and… JEE Main 2026 Full Ray Optics list All JEE Main PYQs