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JEE Main 20244 AprilMorning Shift
Exam
JEE Main
Year
2024
Date
4 April
Shift
Morning Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2024 · 4 April · Morning Shift · Physics · Ray Optics

An effective power of a combination of 5 identical convex lenses...

An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is 25D25 \mathrm{D}. Focal length of each of the convex lens is :

Options

  1. A20 cm20 \mathrm{~cm}
  2. B50 cm50 \mathrm{~cm}
  3. C500 cm500 \mathrm{~cm}
  4. D25 cm25 \mathrm{~cm}

Correct answer

A. 20 cm20 \mathrm{~cm}

Step-by-step solution

We know that Peq=ΣPi∴P_{\mathrm{eq}}=\Sigma \mathrm{P}_{\mathrm{i}} \therefore given all lenses are identical ∴5P=25D∴P=5D∴1f=5⇒f=15 m=20 cm\begin{aligned} & \therefore 5 P=25 D \\ & \therefore P=5 D \\ & \therefore \frac{1}{f}=5 \Rightarrow f=\frac{1}{5} \mathrm{~m}=20 \mathrm{~cm} \end{aligned}
Hence option (1)
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