Differentiate between diffraction and refraction of waves.

Diffraction involves the bending and spreading of waves around obstacles, while refraction is the change in direction of waves passing from one medium to another.

Diffraction is a wave phenomenon that occurs when a wave encounters an obstacle or a slit. It is characterised by the bending of waves around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. In other words, diffraction is the spreading out of waves past openings or around corners. This is most noticeable when the size of the obstacle or opening is comparable to the wavelength of the wave. For instance, when light passes through a narrow slit and is viewed on a screen, a series of light and dark bands are observed. This is due to the interference of light waves diffracted by the slit.

On the other hand, refraction is the change in direction of a wave passing from one medium to another caused by its change in speed. For example, when light travels from air into water, it slows down, causing it to continue to travel with a different direction or path. This bending of light as it passes from one medium to another is what we call refraction. The amount of bending, or angle of refraction, depends on the speeds of light in the two different media. This can be quantified using Snell's law, which relates the ratio of the angle of incidence and the angle of refraction to the ratio of the velocities of the wave in the two different media.

In summary, while both diffraction and refraction involve the bending of waves, they occur under different circumstances. Diffraction occurs when waves encounter obstacles or slits, leading to the spreading out of waves, while refraction occurs when waves pass from one medium to another, leading to a change in direction due to a change in speed.