Assertion `:` A double convex lens `(mu=1.5)` has focal length `10 cm`. When the lens is immersed in water `(mu=4//3)` its focal length becomes `40 cm`.
Reason `:` `(1)/(f)=(mu_(1)-mu_(m))/(mu_(m))((1)/(R_(1))-(1)/(R_(2)))`

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both are false.

Answer

A

Explanation

Focal length of lens immersed in water is four times the focal length of lens in air. It means
`f_(w) = 4f_(a) = 4xx 10` = 40 cm .