Setup: Monochromatic light passes through a single slit of width $a$. On a screen at distance $D$, a diffraction pattern forms.

Central maximum: At $\theta = 0$; brightest and widest feature.

• Linear width: $W = 2\lambda D/a$
• Angular full-width: $2\lambda/a$

Minima (dark fringes): $a\sin\theta = n\lambda$, $n = 1, 2, 3, \ldots$

Secondary maxima: $a\sin\theta \approx (2n+1)\lambda/2$, $n = 1, 2, \ldots$

• Each secondary maximum width: $\lambda D/a$ (half the central maximum width)
• Intensities: 1st $\approx 4.5\%$, 2nd $\approx 1.6\%$ of central maximum

YDSE vs. Single Slit Comparison:

Important NEET trick: In single slit, the condition $a\sin\theta = n\lambda$ gives minima, NOT maxima. Opposite of YDSE!