if for a perfectly symmertical lens, r1=r2, then how will we find focal length??

Asked by Dark | 5th Jan, 2022, 11:54: AM

Expert Answer:

We have Lens maker's formula
 
begin mathsize 14px style 1 over f equals space open parentheses mu space minus space 1 close parentheses open parentheses 1 over r subscript 1 space minus space 1 over r subscript 2 close parentheses end style ............................... (1)
where f is focal length , μ is refractive index of materilal of lens , r1 is radius of curvature of left side
spherical surface and r2 is radius of curvature of right side spherical surface.

numerically r1 = r2 = r, by sign convention r1 is positive and r2 is negative .
 
Hence we get from eqn.(1)
 
begin mathsize 14px style f space equals space fraction numerator r over denominator 2 open parentheses mu minus 1 close parentheses end fraction end style
From the known value of radius of curvature and refractive index of material ,
we get focal length f from above expression

Answered by Thiyagarajan K | 5th Jan, 2022, 01:22: PM