Question

A glass plate of refractive index n = 1.5 and thickness 30 mm is placed just below a wellfocused microscope. For focusing it again, the microscope should be moved through a distance of:

(a) 45 mm 

(b) 30 mm 

(c) 20 mm 

(d) 15 mm 

Answer 1

Correct option (d) 15 mm

Explanation:

The shift in path when an obstacle of refractive index μ and of length is kept in way of a ray is given as

Path difference = (μ - 1) t =  (1.5 - 1)30 mm =15 mm