Assertion: A boconvex lens of focal length `10 cm` is split into two equal parts by a plane parallel to its principle axis. The focal length o fthe each part will be `20 cm`.
Reason: Focal length does not depend on the radii of curvature of two surfaces.

Options

A. If both assertion and reason are true and reason correct explanation of assertion.
B. If both assertion and reason are true but reason the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

D

Explanation

Since, lens is cut into two, equal parts by a plane parallel to its principle axis, so both part still to be biconvex.
Hence, focal length of each part will remain as before i.e., `10 cm`.
Focal length of biconvex lens
`(1)/(f) = (mu - 1) ((1)/(R_(1)) - (1)/(R_(2)))`
where `R_(1)` and `R_(2)` be the radii of curvature of two surfaces.