The diagram is a plan view of a double-slit interference demonstration. $L$ represents a monochromatic light source with a vertical filament. $B$ represents a barrier containing two narrow vertical slits, and $S$ represents a screen on which interference fringes appear. The intensity at the point on the screen at the centre of the fringe pattern is $I$. If one slit is covered, what intensity is found at that same point on the screen?
- A$\frac{I}{\sqrt{2}}$
- B$\frac{I}{2}$
- C$\frac{I}{2\sqrt{2}}$
- D$\frac{I}{4}$