# Waves: Reflection and Refraction

## Waves: Reflection and Refraction

• Waves can be reflected, refracted, or diffracted. The behaviour a wave exhibits depends on the nature of the barrier it encounters.

• Reflection occurs when waves bounce back after hitting a barrier. The Law of Reflection states that the angle of incidence (the angle the incoming wave makes with the normal line) equals the angle of reflexion (the angle the reflected wave makes with the normal line).

• Smooth surfaces, such as mirrors, reflect waves in a regular way where the reflected waves are all parallel. This is called specular reflexion.

• Rough surfaces reflect waves in all directions, and this is known as diffuse reflexion.

• Refraction is the bending of waves as they pass from one medium to another due to a change in speed. Waves will bend towards the normal when they enter a denser medium (like going from air to glass) and away from the normal when they enter a less dense medium (like going from water to air).

• The index of refraction of a material is a measure of how much that material slows down light or other electromagnetic waves.

• Sinusoidal waves such as light or sound often exhibit properties of both reflexion and refraction.

• Refraction can lead to various optical phenomena, including dispersion (splitting up of light into different colours) as seen in prisms and rainbows.

• Refractive index is calculated by dividing the speed of light in vacuum by the speed of light in the medium. The higher the refractive index, the slower the light travels in the medium, and the more it refracts.

• Absolute refractive index is the refractive index relative to vacuum, whereas relative refractive index is the refractive index of one medium relative to another.

• Snell’s law mathematically describes the relationship between the angles and the velocities of the waves. Snell’s Law equation is: n1sin(θ1) = n2sin(θ2), where n1 and n2 are the refractive indices, and θ1 and θ2 are the angle of incidence and angle of refraction, respectively.

• Total internal reflexion occurs when a wave travelling in a dense medium hits the boundary with a less dense medium at an angle greater than the so-called “critical angle” and is completely reflected back into the dense medium. This phenomenon is utilised in fibre optics and prisms.