A plano-convex lens μ = 1.5 has maximum thickness of 1 mm . If the diameter of its aperture is 4 cm , then what is the value of its focal length in the air (in cm )?

Question

A plano-convex lens μ = 1.5 has maximum thickness of 1 mm . If the diameter of its aperture is 4 cm , then what is the value of its focal length in the air (in cm )?,

MARKS App · Accepted Answer

R 2 = 2 2 + R - 0.1 2 ⇒ R 2 = 4 + R 2 + 0.01 - 0.2 R 0 . 2 R = 4 . 0 1 ⇒ R = 4 . 0 1 0 . 2 0 = 4 0 1 2 0 ⇒ R = 2 0 cm from lens formula 1 f = a μ g - 1 ( 1 R 1 - 1 R 2 ) ⇒ 1 f = 1 . 5 - 1 ( 1 2 0 - 1 ∞ ) 1 f = 1 4 0 ⇒ f = 4 0 cm

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