Question

When a thin plate of refractive index 1.5 is placed in the path of one of interfering beams of Michaelson Interferometer, a shift of 30 fringes is observed. If the thickness of plate is 0.018 mm, the wavelength of the used light is ___________

(a) 4000 Å

(b) 5000 Å

(c) 6000 Å

(d) 7000 Å

Answer 1

Right choice is (c) 6000 Å

Easiest explanation: Here, μ = 1.5, n = 30, t = 1.8 X 10^-5 m

Path difference due to the glass plate = 2(μ – 1) t

2(μ – 1) t = nλ

λ = 2(μ – 1) t/n

= 2 X 0.5 X 1.8 X 10^-5/30

= 6000 Å.