WBJEE · Physics · Ray Optics
The least distance of vision of a long sighted person is \(60 \mathrm{cm}\). By using a spectacle lens, this distance is reduced to \(12 \mathrm{cm}\). The power of the lens is
- A \(+5.0 D\)
- B \((20 / 3) \mathrm{D}\)
- C \(-(10 / 3)\) D
- D \(+2.0 \mathrm{D}\)
Answer & Solution
Correct Answer
(B) \((20 / 3) \mathrm{D}\)
Step-by-step Solution
Detailed explanation
Here, \(v=-60 \mathrm{cm}, u=-12 \mathrm{cm}\) \(\therefore\) By using the relation, \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\) We have. \(\frac{1}{f}=\frac{1}{-60}-\frac{1}{-12}\) \(\Rightarrow \quad \frac{1}{f}=\frac{1}{15} \mathrm{cm}\) or \(\frac{100}{15} \mathrm{m}\) So, the…
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