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JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
The image of an illuminated square is obtained on a screen with the help of a converging lens. The distance of the square from the lens is \(40\,cm.\) The area of the image is \(9\,times\) that of the square. The focal length of the lens is........\(cm\)
- A \(36\)
- B \(27\)
- C \(60\)
- D \(30\)
Answer & Solution
Correct Answer
(D) \(30\)
Step-by-step Solution
Detailed explanation
If side of object square \(=\ell\) and side of image square \(=\ell^{\prime}\) From question, \(\frac{\ell^{\prime 2}}{{\ell}^2 }=9\) or \(\quad \frac{\ell^{\prime}}{\ell}=3\) i.e., magnificationm \(=3\) \(\mathrm{u}=-40 \mathrm{cm}\) \(\mathrm{v}=3 \times 40=120\, \mathrm{cm}\)…
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