Final answer:
Diffraction is the spread of waves as they pass through an opening or around an obstacle. This bending is due to the openings being comparable in size to the waves' wavelength. Interference patterns, like double-slit interference in light, can occur when waves diffract through multiple openings.
Step-by-step explanation:
When a wave passes through a small opening and spreads out to fill the space beyond the opening, the phenomenon is known as diffraction. Diffraction occurs because the width of the opening is comparable to the wavelength of the waves, leading to the bending of the wave around the edges of the aperture. This is observable with various types of waves, including sound waves and water waves. Sound, for example, will be heard throughout a room even if it enters through a small opening like a door, owing to its wavelength being similar to the size of the opening and hence causing it to diffract.
Interference patterns can also be observed when waves pass through a set of openings whose spacing is comparable to their wavelength. A familiar example is the double-slit interference of light, where monochromatic light passing through two slits produces a pattern due to the interference of diffracted waves.
For light waves, diffraction is less noticeable in everyday situations because light has much shorter wavelengths compared to the size of typical openings. However, when light passes through very small slits, it too exhibits diffraction, bending around the edges similarly to sound. The bending of light through narrower slits can be explained using Huygens's principle, which treats every point on a wavefront as a source of secondary spherical wavelets.