Ray Optics

JEE Main level, single correct, medium

274 of 295

Question 274 of 295

In a microscope of tube length 10 cm two convex lenses are arranged with focal length of 2 cm and 5 cm. Total magnification obtained with this system for normal adjustment is (5)k(5)^{k}. The value of kk is ____\_\_\_\_.

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Answer: (B) 2

For a microscope in normal adjustment, magnification is given by M=Lfo×DfeM = \frac{L}{f_o} \times \frac{D}{f_e}
where LL is tube length (10 cm), fof_o is objective focal length (2 cm), fef_e is eyepiece focal length (5 cm), and DD is least distance of distinct vision (25 cm).
M=102×255=5×5=25=52M = \frac{10}{2} \times \frac{25}{5} = 5 \times 5 = 25 = 5^2
Therefore, k=2k = 2

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