Diameter of plano-convex lens is 6 cm and thickness at the centre is 3 mm . If speed of light in material of l

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Diameter of plano-convex lens is 6 cm and thickness at the centre is 3 mm . If speed of light in material of lens is 2 × 10^8 m/s , the focal length of the lens is:

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![image](https://pub-7faa453bd1ec4bf0a04cc031c6f058de.r2.dev/images/910503b6-c6bd-471d-8b07-15efb3dc8031.png) 1. Refractive index μ = c/v = 3 × 10^8/2 × 10^8 = 1.5 .2. Geometry of lens: Let R be radius of curvature. R^2 = (R - t)^2 + r^2 where t = 0.3 cm and r = 3 cm . R^2 = R^2 - 2Rt + t^2 + r^2 2Rt = t^2 + r^2 .Since t is small, 2Rt ≈ r^2 2R(0.3) = 9 0.6R = 9 R = 15 cm .3. Lens Maker's Formula: 1/f = (μ - 1)(1/R_1 - 1/R_2) .For plano-convex: R_1 = 15 cm, R_2 = ∞ . 1/f = (1.5 - 1)(1/15 - 0) = 0

Diameter of plano-convex lens is $6 cm$ and thickness at the centre is $3 mm$ . If speed of light in material of lens is $2 \times 1 0^{8} m/s$ , the focal length of the lens is:

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Diameter of plano-convex lens is 6cm and thickness at the centre is 3mm. If speed of light in material of lens is 2×108m/s, the focal length of the lens is: