In a compound microscope, the focal length of the objective and the eye lens are `2.5 cm` and `5 cm` respectively. An object is placed at `3.75cm` before the objective and image is formed at the least distance of distinct vision, then the distance between two lenses will be `( i.e.` length of the microscope tube )

Options

A. 11.67 cm
B. 12.67 cm
C. 13.00 cm
D. 12.00 cm

Answer

A

Explanation

L `= v_(o) + u_(e)`
For objective lens-
`(1)/(v_(o)) = (1)/(2.5) - (1)/(3.75) [ (1)/(v_(o)) - (1)/(u_(o)) = (1)/(f_(o))] `
`v_(o) = 7.5 ` cm
For eye lens -
`(1)/(u_(e)) = (-1)/(25) - (1)/(5) = -4.16 `cm
`therefore " " L = 7.5 + | -4.16| = 11.67 ` cm.