Answer to Question #132197 in Optics for Adigun Abimbola

Question

An observer with a near point of 25cm looks through a microscope with an objective lens of focal length 1.2cm. when an object is placed 1.28cm from the objective, the angular magnification is -198 and the final image is formed at infinity a. What is the tube length of the microscope b. What is the focal length of the eyepiece

Answer 1

The angular magnification of the eyepiece is

$$M=1+\frac{d}{f_e},$$

the focal length of the eyepiece is

$$f_e=\frac{d}{M-1}=\frac{25}{198-1}=0.127\text{ cm}.$$