Question

While conducting the Young's double slit experiment, a student replaced the two slits with a large opaque plate in the x-y plane containing two small holes that act as two coherent point sources $(S_1,S_2)$ emitting light of wavelength 600 nm. The student mistakenly placed the screen parallel to the $x-z$ plane (for $z>0$) at a distance $D=3m$, from the mid-point of $S_1,S_2$, as shown schematically in the figure. The distance between the sources $d=0.6003mm$. The origin O is at the intersection of the screen and the line joining $S_1,S_2$. Which of the following is(are) true of the intensity pattern on the screen?

• A. Semi circular bright and dark bands centered at point O
• B. The region very close to the point O will be dark
• C. Straight bright and dark bands parallel to the x-axis
• D. Hyperbolic bright and dark bands with foci symmetrically placed about O in the x-direction.

Answer 1

Answer: (A), (B)

The correct options are
A The region very close to the point O will be dark
B Semi circular bright and dark bands centered at point O

Fringes will be semi circular from YDSE theory.

$\frac{d}{\lambda }=1000+\frac{1}{2}$

At O, $\Delta x=1000\lambda +\frac{\lambda }{2}$

Hence it will be dark at O.

Answer is A and B.