CBSE Class 12-science Answered
17th sum
Asked by lovemaan5500 | 07 Dec, 2019, 08:52: PM
Expert Answer
We have, lens maker's formula as given below
where f is focal length , μ is refractive index, R1 is the radius of curvature of left side surface
and R2 is the radius of curvature of right side surface.
If radius of curvature R1 = R2 = R and by cartesian sign convention,we rewrite lens maker formaula as
1/f = (μ -1) ( 2/R) = 1/20 ........................(1)
If the lens is cut into half using the plane passing through AB, radius of curvature of right surface becomes infinity and (1/R2) will be zero.
Hence lens makers formula for plano-convex lens becomes, 1/f1 = (μ -1) ( 1/R) ................(2)
f1 is new focal length, from eqn.(1) and (2), we get, 1/f1 = 1/40 or new focal length f1 = 40 cm
-------------------------------------
if lens is split into half by a plane passing through CD, there is no change in radii of curvature.
Hence no change in focal length . But less amount of light ray from object is collected by lens , hence intensity of image is reduced
Answered by Thiyagarajan K | 07 Dec, 2019, 10:07: PM
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