25. In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16 cm and 9 cm respectively. What is the actual distance of separation ?

25. In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16 cm and 9 cm respectively. What is the actual distance of separation ?

(a) 12.5 cm

(b) 12 cm

(c) 13 cm

(d) 14 cm

Answer :  (b) 12 cm

\(h_0 = \sqrt{h_1 h_2}\)

\(= \sqrt{16 \times 9}\)

\(= 12 \,\text{cm}\)