Optics Question 873
Question: A double slit, $ S _{1}-S _{2} $ is illuminated by a light source S emitting light of wavelength $ \lambda $ . The slits are separated by a distance d. A plane mirror is placed at a distance D in front of the slits and a screen is placed at a distance 2D behind the slits. The screen receives light reflected only by the plane mirror. The fringe-width of the interference pattern on the screen is
Options:
A) $ \frac{D\lambda }{d} $
B) $ \frac{2D\lambda }{d} $
C) $ \frac{3D\lambda }{d} $
D) $ \frac{4D\lambda }{d} $
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Due to reflection virtual source will be formed at distance D from mirror.
The effective distance of the screen $ =2D+2D=4D $
$ \therefore $ Fringe width $ =\frac{4D\lambda }{d} $
