JEE Main 2014 · 11 Apr · Shift 1 · Physics Q25

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In a compound microscope the focal length of objective lens is 1.2 cm and focal length of eye piece is 3.0 cm. When object is kept at 1.25 cm in front of objective, final image is formed at infinity. Magnifying power of the compound microscope should be :

200

100

400

150

Answer and worked solution

Official answer: A

Objective. $v=\dfrac{uf}{u-f}=\dfrac{1.25\times1.2}{0.05}=30$ cm, so $m_o=\dfrac{30}{1.25}=24$ .

Eyepiece (final image at infinity): $\dfrac{25}{3}=8.33$ .

$M=24\times8.33=200$ .

Topics:Optical instruments

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JEE Main 2014 · 11 Apr · Shift 1, Physics question 25