The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. Its focal length is 12 cm. What is the refractive index of the material of the lens?

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(3) 1.50. Given: double convex lens, faces of radius 10 cm and 15 cm, focal length f = 12 cm. Idea: for a double convex lens the first face is convex towards the incoming light and the second away from it, so R₁ = +10 cm and R₂ = -15 cm. 1/(R₁)-1/(R₂) = 1/(10)+1/(15) = 1/6 cm⁻¹ Lens maker's formula: 1/(12) = (n-1)×1/6. So n-1 = 6/(12) = 0.5 and n = 1.50. The refractive index of the material is 1.50.

The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. Its focal length is 12 cm. What is the refractive index of the material of the lens?

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