MHT CET · Physics · Ray Optics
A plano convex lens fits exactly in to a plano concave lens. Their plane surfaces are parallel to each other. Lenses are made up of different materials of refractive indices ' \(n_1\) ' \(n_2\) ' and ' \(R\) ' is the radius of curvature of the curved surface of lenses. Focal length of the combination is
- A \(\frac{\mathrm{R}}{\mathrm{n}_1+\mathrm{n}_2}\)
- B \(\frac{2 \mathrm{R}}{\mathrm{n}_1-\mathrm{n}_2}\)
- C \(\frac{\mathrm{R}}{2\left(\mathrm{n}_1-\mathrm{n}_2\right)}\)
- D \(\frac{\mathrm{R}}{\mathrm{n}_1-\mathrm{n}_2}\)
Answer & Solution
Correct Answer
(D) \(\frac{\mathrm{R}}{\mathrm{n}_1-\mathrm{n}_2}\)
Step-by-step Solution
Detailed explanation
\(\frac{1}{f_1} = (n_1-1)\left(\frac{1}{\infty} - \frac{1}{-R}\right) = \frac{n_1-1}{R}\) \(\frac{1}{f_2} = (n_2-1)\left(\frac{1}{-R} - \frac{1}{\infty}\right) = -\frac{n_2-1}{R}\)
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