JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
The distance between object and its \(3\) times magnified virtual image as produced by a convex lens is \(20 \mathrm{~cm}\). The focal length of the lens used is _______ \(\mathrm{cm}\).
- A \(20\)
- B \(14\)
- C \(15\)
- D \(30\)
Answer & Solution
Correct Answer
(C) \(15\)
Step-by-step Solution
Detailed explanation
\(\mathrm{v}=3 \mathrm{u}\) \(\mathrm{v}-\mathrm{u}=20 \mathrm{~cm}\) \(2 \mathrm{u}=20 \mathrm{~cm}\) \(\mathrm{u}=10 \mathrm{~cm}\) \(\frac{1}{(-30)}-\frac{1}{(-10)}=\frac{1}{\mathrm{f}}\) \(\mathrm{f}=15 \mathrm{~cm}\)
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