Question

An object viewed from a near point distance of $25\text{cm}$, using a microscopic lens with magnification $6$, gives an unresolved image. A resolved image is observed at infinite distance with a total magnification double the earlier using an eyepiece along with the given lens and a tube of length $0.6\text{m}$, if the focal length of the eyepiece is equal to _____ $\text{cm}$.

• A. 25
• B. 25.00
• C. 25.0

Answer 1

Answer: (A), (B), (C)

For simple microscope,

$m=1+\frac{D}{f_0}$

$\Rightarrow 6=1+\frac{25}{f_0}$

$\Rightarrow f_0=5\text{cm}$

For compound microscope,

$m^{\prime }=\frac{lD}{f_0{f}_e}$

$\Rightarrow 12=\frac{60\times 25}{5\times f_e}$

$\Rightarrow f_e=25\text{cm}$