Among the three phenomena you mentioned—refraction, reflection, and diffraction—only diffraction directly affects the frequency of waves. Refraction and reflection do not change the frequency of waves but can alter other properties such as the direction or intensity of the wave.
Refraction: Refraction is the bending of waves as they pass from one medium to another with different optical densities. While refraction changes the direction of waves, it does not alter their frequency. The frequency remains the same before and after refraction.
Reflection: Reflection occurs when waves bounce off a surface and change direction. It involves a change in the wave's direction but not its frequency. When a wave reflects, it undergoes a reversal in direction, but the frequency remains constant.
Diffraction: Diffraction is the bending or spreading of waves around obstacles or through openings. Unlike refraction and reflection, diffraction can affect the frequency of waves to some extent. When waves encounter an obstacle or pass through a narrow opening, diffraction can cause changes in the intensity and distribution of the wave, which might indirectly affect the perception of frequency.
However, it is important to note that diffraction does not inherently change the frequency itself. The frequency remains the same before and after diffraction, but the wavefronts may experience modifications in shape and direction due to the interaction with obstacles or openings.
In summary, while refraction and reflection do not change the frequency of waves, diffraction can cause alterations in the wave's behavior, but not the frequency directly.