In a double slit experiment the distance between the slits is 0.1 cm and the screen is placed at 50 cm from the slits plane. When one slit is covered with a transparent sheet having thickness t and refractive index n (= 1.5), the central fringe shifts by 0.2 cm. The value of t is cm.
- 6.0 10-3
- 8 10-4
- 5.0 10-3
- 5.6 10-4
Answer
(2) 8 10-4
Solution
The sheet introduces an extra optical path (n - 1)t, so the central fringe shifts by
y = (n - 1)tDd
t = y d(n - 1)D = 0.2 0.1(1.5 - 1) 50
t = 0.0225 = 8 10-4 cm
Answer: (2)