UPSC NDA II 2018 General Ability Solved Paper

Concept:Microscopes and telescopes both use two convex lenses (objective and eyepiece).Magnification formulas differ: for a microscope, $M = \frac{L}{f_o}\left(\frac{D}{f_e}\right)$; for a telescope, $M = \frac{f_o}{f_e}$.$f_o$ = focal length of objective, $f_e$ = focal length of eyepiece, $L$ = tube length, $D$ = least distance of distinct vision.Explanation:Statement 1: Both eyepiece and objective of a microscope are convex lenses. This is true.Statement 2: In a telescope, the objective has a larger focal length than the eyepiece. This is true.Statement 3: Telescope magnification $M = f_o / f_e$; as $f_o$ increases, $M$ increases. So statement 3 is correct.Statement 4: Microscope magnification $M = \frac{L}{f_o}\left(\frac{D}{f_e}\right)$; as $f_o$ increases, $M$ decreases. So statement 4 is false.Thus correct statements are 1, 2, and 3.Answer:D. 1, 2 and 3