Question

In a double slit experiment instead of taking slits of equal widths, one slit is made twice as wide as the other, then in the interference pattern

• A. the intensities of both the maxima and the minima increases
• B. the intensity of the maxima increases and the minima has zero intensity
• C. the intensity of maxima decreases and that of minima increases
• D. the intensity of maxima decreases and the minima has zero intensity

Answer 1

Answer: (A)

In interference we know that
$I_{max}=(\sqrt{I_1}+\sqrt{I_2}{)}^2$
and $I_{min}=(\sqrt{I_1}-\sqrt{I_2}{)}^2$
Under normal conditions (when the widths of both the slits
are equal)
$I_1=I_2=I$ (say)
$\therefore I_{max}=4Iand{I}_{min}=0$
When the width of one of the slits is increased. Intensity due
to that slit would increase, while that of the other will remain
same. So, let:
$I_1=I$
and $I_2=\eta I(\eta >1)$
Then, $I_{max}=I(1+\sqrt{\eta }{)}^2>4I$
and $I_{min}=I(\sqrt{\eta }-1{)}^2>0$
$\therefore$ Intensity of both maxima and minima is increased.