what will be the focal lenght of the lens if radii of curvature of two surfaces were equal in magnitude and also had the same sign?

Asked by Jahanvi | 8th Oct, 2015, 07:41: PM

Expert Answer:

The focal length of a lens is related to the radii of curvatures according to the lens maker's formula as:
 
begin mathsize 14px style 1 over straight f equals open parentheses straight n minus 1 close parentheses open parentheses 1 over straight R subscript 1 minus 1 over straight R subscript 2 close parentheses end style
Now, if R1 = R2 both in magnitude and sign, then begin mathsize 14px style 1 over straight R subscript 1 minus 1 over straight R subscript 2 equals 0 end style
Therefore, 1/f = 0 and so f = ∞

This scenario is however not feasible practically and both R1 and R2 will have opposite signs or they will have different magnitudes if they are of the same sign.

Answered by Romal Bhansali | 9th Oct, 2015, 12:28: PM