The diagram gives a plan view of a double-slit interference setup. $L$ is a monochromatic light source with a vertical filament. $B$ is a barrier containing two thin vertical slits and $S$ is a screen on which interference fringes are produced. The intensity is $I$ at a point on the screen where the centre of the fringe pattern is formed. What is the intensity, at that same point, when one slit is blocked?
- A$\frac{I}{\sqrt{2}}$
- B$\frac{I}{2}$
- C$\frac{I}{2\sqrt{2}}$
- D$\frac{I}{4}$