JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
To find the focal length of a convex mirror, a student records the following data
| Object Pin | Convex Lens | Convex Mirror | Image Pin |
| \(22.2\,cm\) | \(32.2\,cm\) | \(45.8\,cm\) | \(71.2\,cm\) |
- A \(f_1 = 7.8\,cm\,\,\,\,\, f_2 = 12.7\,\,cm\)
- B \(f_1 = 12.7\,cm\,\,\,\,\, f_2 = 7.8\,\,cm\)
- C \(f_1 = 15.6\,cm\,\,\,\,\, f_2 = 25.4\,\,cm\)
- D \(f_1 = 7.8\,cm\,\,\,\,\, f_2 = 25.4\,\,cm\)
Answer & Solution
Correct Answer
(A) \(f_1 = 7.8\,cm\,\,\,\,\, f_2 = 12.7\,\,cm\)
Step-by-step Solution
Detailed explanation
From lens \(u_{1}=-(32.2-22.2) c m=-10 c m\) \(v_{1}=(71.2-32.2) \mathrm{cm}=39 \mathrm{cm}\) \(\frac{1}{f_{1}}=\frac{1}{v_{1}}-\frac{1}{u_{1}}=\frac{1}{36}+\frac{1}{10}=\frac{49}{390}\) or \(f_{1}=\frac{390}{49} \mathrm{cm}=7.8 \mathrm{cm}\) For mirror…
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