Question

In a compound microscope, the focal lengths of two lenses are 1.5 cm and 6.25 cm an object is placed at 2 cm form objective and the final image is formed at 25 cm from eye lens. The distance between the two lenses is

• A. 6.00 cm
• B. 7.75 cm
• C. 9.25 cm
• D. 11.00 cm

Answer 1

Answer: (D)

11.00 cm

Answer 2

It is given that f_o = 1.5 cm, f_e = 6.25 cm, u_o = 2 cm

When final image is formed at least distance of distinct vision, length of the tube $L _ { D } = \frac { u _ { o } f _ { o } } { u _ { o } - f _ { o } } + \frac { f _ { e } D } { f _ { e } + D }$

⇒ $L _ { D } = \frac { 2 \times 1.5 } { ( 2 - 1.5 ) } + \frac { 6.25 \times 25 } { ( 6.25 + 25 ) } = 11 \mathrm {~cm}$.