Question 328: Ray Optics

Question

In a compound microscope, the magnified virtual image is formed at a distance of 25 cm from the
eye-piece. The focal length of its objective lens is 1 cm. If the magnification is 100 and the tube
length of the microscope is 20 cm, then the focal length of the eye-piece lens (in cm) is __________.

Accepted Answer

L = 20, f
0
= 1cm, M = 100
$$M = {{{v_0}} \over {{u_0}}}\left( {1 + {D \over {{f_e}}}} ight)$$
$$ 	herefore $$ $$M = {L \over {{f_0}}}\left( {1 + {D \over {{f_e}}}} ight)$$ [v
0
$$ \approx $$ L, u
0
$$ \approx $$ f
0
]
$$ \Rightarrow $$ $${{20} \over 1}\left( {1 + {{25} \over {{f_e}}}} ight)$$ = 100
on solving we get
f
e
= 6.25 cm

Ray Optics

In a compound microscope, the magnified virtual image is formed at a distance of 25 cm from the eye-piece. The focal length of its objective lens is 1 cm. If the magnification is 100 and the tube length of the microscope is 20 cm, then the focal length of the eye-piece lens (in cm) is __________.

Choose the correct answer: