= Solution
With $w=1.0\,\mathrm{\mu m}$ the order positions are unchanged from the <grating equation>, and the envelope's first zeros satisfy $|\sin\theta|=\lambda/w$. Equivalently the first missing integer orders are \b[$m=\pm5$]. The third-order peaks remain appreciable. The displayed order-coordinate $s=p\sin\theta/\lambda$ places all principal maxima at integers.
\Image[/past-exam-of-the-physics-a-course-of-the-university-of-cambridge/2011/paper-1-grating-widths.png]
{title=Slit-width envelopes on a common incident-intensity scale}
{description=Original finite-array model with an illustrative 60 illuminated slits to make the peaks visible. Dashed lines show single-slit envelopes; the supplied slit pitch and widths set the peak ratios independently of this illustrative slit count.}
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