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 $I_0$. If one of the slits closed, the intensity at this point will be

• A. $I_0$
• B. $I_0/4$
• C. $I_0/2$
• D. $4I_0$

Answer 1

Answer: (B)

$I_0/4$

For interference of two waves,

$I_{total}=I_1+I_2+2\sqrt{I_1{I}_{2}cos\theta }$

For equal intensities and central fringe,

$I_{total}=4I_1=I_0$........given

$\therefore$ $I_1=\frac{I_0}{4}$

Hence, when one slit is closedthe intensity will be $\frac{I_0}{4}$