Verified Solution • 2025–26 Session moderate

QJEEM20Ph947f: JEE Main 2020 Physics - Class 12 JEEM20Ph947f Solution: In a compound microscope, the magnified virtual image is formed …

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 __________.

Step-by-Step Verified Solution

L = 20, f0 = 1cm, M = 100

M=v0u0(1+Dfe)M = {{{v_0}} \over {{u_0}}}\left( {1 + {D \over {{f_e}}}} \right)

∴\therefore M=Lf0(1+Dfe)M = {L \over {{f_0}}}\left( {1 + {D \over {{f_e}}}} \right) [v0 ≈\approx L, u0 ≈\approx f0]

⇒\Rightarrow 201(1+25fe){{20} \over 1}\left( {1 + {{25} \over {{f_e}}}} \right) = 100

on solving we get

fe = 6.25 cm

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