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A Double Convex Lens Has Two Surfaces of Equal Radii R and Refractive Index M = 1 ⋅ 5 - Science

MCQ

A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]

Options

  • \[f = R/2\] 

  • \[f = R\]
  • \[f = - R\]

  • \[f = 2R\]

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Solution

f = R
As from lens maker formula:
\[\frac{1}{f} = (m - 1)(\frac{1}{R_1} - \frac{1}{R_2})\]
\[ \Rightarrow \frac{1}{f} = (1 . 5 - 1)(\frac{1}{R} - \frac{1}{- R}) (\text{ As given } R_1 = R_2 = R)\]
\[ \frac{1}{f} = (0 . 5)(\frac{1}{R} + \frac{1}{R})\]
\[ \frac{1}{f} = (0 . 5)(\frac{2}{R})\]
\[ f = R\]

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APPEARS IN

HC Verma Class 11, 12 Concepts of Physics 1
Chapter 18 Geometrical Optics
MCQ | Q 9 | Page 411
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