A watchmaker requires a simple magnifier for close inspection of miniature gears.
PHYSICS · Multi-part · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
A watchmaker requires a simple magnifier for close inspection of miniature gears.
(a) He desires a magnifying power of 12 with his eye completely relaxed (final image at infinity). Find the focal length of the lens that he should purchase. Take the least distance of distinct vision for a normal eye as 25cm.
(b) Optical suppliers list focal lengths in millimetres. Express your answer of part (a) in millimetres.
(c) After several years, the watchmaker’s near point recedes to 40cm. Using the same lens, calculate the magnifying power he will now obtain for the same viewing condition (final image at infinity).