When the wavelength of a wave is on the same order of magnitude as the size of an opening or a slit through which it passes, a phenomenon known as diffraction occurs. Diffraction refers to the bending and spreading of waves as they encounter obstacles or pass through narrow openings.
If the wavelength of a wave is similar to the size of the slit, the wavefronts will diffract significantly as they pass through the opening. This diffraction effect causes the wave to spread out and exhibit interference patterns. The specific pattern produced depends on the geometry of the slit and the characteristics of the wave.
In the case of light waves passing through a slit with a comparable size, you would observe a diffraction pattern known as the single-slit diffraction pattern or the Fraunhofer diffraction pattern. This pattern consists of a central bright region called the central maximum, flanked by alternating dark and bright regions called fringes or secondary maxima.
The width of the central maximum is larger compared to the secondary maxima, and the intensity gradually decreases as you move away from the central maximum. The overall diffraction pattern is a result of interference between the diffracted waves from different parts of the slit. The width of the slit and the wavelength of the light determine the precise characteristics of the diffraction pattern.
In summary, when the wavelength of a wave is comparable to the size of a slit or opening, diffraction occurs, resulting in the spreading and interference of the wave, leading to observable patterns such as the single-slit diffraction pattern.