Question

The slits in a Young’s double slit experiment have equal widths and the source is placed symmetrically relative to the slits. The intensity at the central fringes is I₀. If one of the slits is closed, the intensity at this point will be

• A. I₀
• B. $I_{0}/4$
• C. $I_{0}/2$
• D. $4I_{0}$

Answer 1

Answer: (B)

$I_{0}/4$

Answer 2

By using $I_{R} = 4I\cos^{2}\frac{\varphi}{2}$ {where I = Intensity of each wave}

At central position φ = 0⁰, hence initially I₀ = 4I.

If one slit is closed, no interference takes place so intensity at the same location will be I only i.e. intensity become s$\frac{1}{4}th$ or $\frac{I_{0}}{4}$.