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JEE Main 20257 AprilMorning Shift
Exam
JEE Main
Year
2025
Date
7 April
Shift
Morning Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2025 · 7 April · Morning Shift · Physics · Ray Optics

Two thin convex lenses of focal length 30 cm and 10 cm are placed...

Two thin convex lenses of focal length 30 cm and 10 cm are placed coaxially, 10 cm apart. The power of this combination is :

Options

  1. A5 D
  2. B1 D
  3. C20 D
  4. D10 D

Correct answer

D. 10 D

Step-by-step solution

f1=30 cm,f2=10 cm\mathrm{f}_1=30 \mathrm{~cm}, \mathrm{f}_2=10 \mathrm{~cm}
1feq=1f1+1f2−df1f2, d=\frac{1}{\mathrm{f}_{\mathrm{eq}}}=\frac{1}{\mathrm{f}_1}+\frac{1}{\mathrm{f}_2}-\frac{\mathrm{d}}{\mathrm{f}_1 \mathrm{f}_2}, \mathrm{~d}= distance between lens
1feq=10.3+10.1−0.1(0.3)(0.1)\frac{1}{\mathrm{f}_{\mathrm{eq}}}=\frac{1}{0.3}+\frac{1}{0.1}-\frac{0.1}{(0.3)(0.1)}
1feq=10.1\frac{1}{\mathrm{f}_{\mathrm{eq}}}=\frac{1}{0.1}
Power =1feq=10D=\frac{1}{\mathrm{f}_{\mathrm{eq}}}=10 \mathrm{D}
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