Geometrical OpticsHard
Question
Diameter of a plano-convex lens is 6cm and thickness at the center is 3 mm. If speed of light in material of lens is 2 × 108 m/s, the focal length of the lens is :
Options
A.15 cm
B.20 cm
C.30 cm
D.10 cm
Solution
From trigonometry,
R2 = (3)2 + (R- 0.3)2
∴ from Lens-Maker formula,
f = 30cm
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