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JEE Mains · Physics · STD 12 - Ray optics and optical instruments
  • JEE Mains 2019
  • Hard
  • MCQ

What is the position and nature of image formed by lens combination shown in figure? (\(f_1, f_2\) are focal lengths)

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Answer & Solution

Correct Answer

(D) \(70\, cm\) from point \(B\) at right ; real

Step-by-step Solution

Detailed explanation

Image by convex lens:

\(\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\) ;    \(\frac{1}{v} + \frac{1}{{20}} = \frac{1}{5}\)

\({v=\frac{20}{3}\, \mathrm{cm}}\)

Image by concave lens:

\(u=\left[\frac{20}{3}-2\right]=\frac{14}{3} \,\mathrm{cm}\)

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) ;   \(\frac{1}{v}-\frac{3}{14}=-\frac{1}{5}\)

\(v=70\, \mathrm{cm}\)

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