|Jun23-06, 03:02 PM||#1|
Focal length of plano convex lens
# Diameter of a Plano-convex lens is 6 cm and the thickness at the center is 3 mm. If the speed of light in the material of the lens is 2 x 10^8 m/sec, what is the focal length of the lens?
I solved it in the following way:
Let R be the radius of curvature of the convex surface.
Given that AB = 3 mm = 0.3 cm, AD = CD/2 = 3 cm, refractive index(n) = 1.5
By the property of circles,
AB = (AD^2)/(2R)
Therefore, R = (AD^2)/(2AB)
= 9/(2 x 0.3)
= 15 cm
According to thin lens formula,
1/f = (n – 1)/R
Solving I get,
f = 30 cm
Is it right?
|Jun25-06, 11:28 PM||#2|
|Jun26-06, 11:48 AM||#3|
Thanks for your help.
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