JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
In an experiment a convex lens of focal length \(15\, cm\) is placed coaxially on an optical bench in front of a convex mirror at a distance of \(5\,cm\) from it. It is found that an object and its image coincide, if the object is placed at a distance of \(20\,cm\) from the lens. The focal length of the convex mirror is.......\(cm\)
- A \(27.5\)
- B \(20\)
- C \(25\)
- D \(30.5\)
Answer & Solution
Correct Answer
(A) \(27.5\)
Step-by-step Solution
Detailed explanation
Given, focal kngth of lens \((\mathrm{f})=15 \,\mathrm{cm}\) object is placed at a distance \((u)=-20\, \mathrm{cm}\) By lens formula, \(\frac{1}{f} = \frac{1}{v} - \frac{1}{u}\) \(\frac{1}{v} = \frac{1}{f} + \frac{1}{u}\) \( = \frac{1}{{15}} - \frac{1}{{20}}\)…
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