# Answer to Question #42273 in Optics for qwerty

Question #42273

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

(1) 30 cm

(2) 20 cm

(3) 10 cm

(4) 40 cm

(1) 30 cm

(2) 20 cm

(3) 10 cm

(4) 40 cm

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