JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
Diameter of a plano-convex lens is \(6 \,cm\) and thickness at the centre is \(3\, mm\). If the speed of light in the material of the lens is \(2 \times 10^8 m/sec\), the focal length of the lens is.......\(cm\)
- A \(15 \)
- B \(20\)
- C \(30\)
- D \(10\)
Answer & Solution
Correct Answer
(C) \(30\)
Step-by-step Solution
Detailed explanation
According to lens formula \(\frac{1}{f} = (\mu - 1)\left[ {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right]\) The lens is plano-convex i.e., \({R_1} = R\) and \({R_2} = \infty \) Hence \(\frac{1}{f} = \frac{{\mu - 1}}{R} \Rightarrow f = \frac{R}{{\mu - 1}}\) Speed of light in…
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