Two identical glass `(mu_(g)=3//2)` equi- convex lenses of focal length f each are kept in contact. The space between the two lenses is also filled with water `(mu_(g)=4//3).` The focal length of the combination is

Options

A. `(3f)/(4)`
B. `(f)/(3)`
C. f
D. `(4f)/(3)`

Answer

A

Explanation

Radius of curvature` R_(1) = R_(2) = R `

`(1)/(f) = ((3)/(2) - 1) (2)/(R ) = (1)/( R) , " " therefore ` R = f
`(1)/(f) = ((4)/(3) -1 ) { - (2)/(R ) } =- (2)/(3R)`
So, `(1)/(f_(eq)) - (1)/(f) - (2)/(3f) rArr (3-2+ 3)/(3f) = (4)/(3f)`
`f_(eq) = (3f)/(4).