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A plano-convex lens has a diameter of 6 cm and a central thickness of 3 mm. If the speed of light in the lens material is 2 × 10⁸ m/s, what is the focal length of the lens?

1. 15 cm
2. 20 cm
3. 30 cm
4. 10 cm

Correct answer: 30 cm

Solution

The focal length of a plano-convex lens can be calculated using the lensmaker's equation, which takes into account the curvature of the lens surfaces and the refractive index of the material. Given the parameters, the calculated focal length is 30 cm, which aligns with the properties of the lens and the speed of light in the material.

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