Answer
4
Work Step by Step
We use equation (36-3) for a single-slit experiment;
$\alpha \sin \theta = m \lambda $ where $m=1,2,3,....$ (minima)
Therefore,
$\alpha \sin \theta = 4 \lambda $
This means that $m=4$. Also, the point is a minimum.
According to the phasor diagram (Fig 36-7) we should see a complete circle for each minima, for a total of 4 overlapping circles.
