Reflection and Refraction

“Reflection” refers to the phenomenon when waves, including light and sound, bounce off a surface. For example, when light waves strike a mirror, they get reflected back.
The initial wave is known as the “incident wave”, and after it hits the reflective surface, it becomes the “reflected wave”.
In reflexion, the angle at which the wave hits the surface (angle of incidence) is the same as the angle at which it leaves the surface (angle of reflexion). This law is also known as the “law of reflexion”.
The normal line, an imaginary line drawn perpendicular to the reflective surface, is used to measure these angles.
“Refraction” refers to the change in direction and speed of a wave as it passes from one medium to another. This happens because waves travel at different speeds in different media.
As an example, when light passes from air into glass, it slows down and bends towards the normal. It then speeds up and bends away from the normal when exiting the glass.
Unlike reflexion, refraction does not follow a simple rule regarding angles. The extent of bending, or change in direction, depends on the speeds of the wave in the two media.
The measure of a material’s power to refract light is called its refractive index. The formula to calculate the refractive index (n) is n = sin(i)/sin(r), where ‘i’ is the angle of incidence and ‘r’ is the angle of refraction.
Total Internal Reflection (TIR) is a phenomenon that occurs when a wave travelling in a dense medium hits the boundary with a less dense medium at an angle greater than its ‘critical angle’, it is completely reflected within the denser medium. This is how fibre optics work.
In normal cases, refraction causes waves to spread out or bend around objects and openings in their path. This is known as diffraction.
The extent of diffraction depends on the size of the gap or obstacle and the wavelength of the wave. Larger wavelengths diffract more.
All kinds of waves, including light, sound, water, and electromagnetic waves like microwaves and radio waves, can undergo reflexion, refraction, and diffraction.