Reflection of Light Overview

Reflection of Light: Overview

• Reflection of light is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.
• The angle of incidence is equal to the angle of reflection. This is known as the law of reflection.
• Light reflects off surfaces in a predictable manner, based on the angle of incidence and the properties of the reflecting surface.
• This property is fundamental to our ability to see objects.

The Law of Reflection

• The incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.
• The angle of incidence (θ_i) is the angle between the incident ray and the normal.
• The angle of reflection (θ_r) is the angle between the reflected ray and the normal.
• The law states that θ_i = θ_r.

Types of Reflection

• Specular Reflection: Reflection from a smooth surface, resulting in a clear, focused image. Examples include mirrors. Rays bounce off in a predictable manner.
• Diffuse Reflection: Reflection from a rough surface, resulting in scattered light. Example: The surface of a wall or paper. Rays bounce off in various directions.

Factors Affecting Reflection

• Surface smoothness: Smooth surfaces produce specular reflection, while rough surfaces cause diffuse reflection.
• Material properties: The nature of the material (e.g., colour, texture) can influence how light is reflected. Dark surfaces absorb more light, whereas light coloured surfaces reflect more light, than the material itself.
• Angle of incidence: The angle at which light strikes the surface affects the angle at which it is reflected. Greater angles result in greater angles of reflection.

Applications of Reflection

• Mirrors: Used for creating images, in telescopes, and in many other optical devices.
• Concave mirrors: Can concentrate light, used in headlights and searchlights.
• Convex mirrors: Used in side-view mirrors of vehicles, providing a wider field of view.
• Optical fibers: Utilize the principle of total internal reflection (TIR) to transmit light signals over long distances and around curves.

Total Internal Reflection (TIR)

• TIR occurs when light travelling from a denser medium to a less dense medium at an angle greater than the critical angle is completely reflected back into the denser medium.
• The critical angle is the angle of incidence that produces an angle of refraction of 90 degrees.
• TIR is crucial to the operation of fiber optic cables, and some medical instruments.

Image Formation by Mirrors

• Plane Mirrors: Create virtual images that are upright, laterally inverted, and the same size as the object. The image is located the same distance behind the mirror as the object is in front.
• Concave Mirrors: Produce both real and virtual images, depending on the position of the object relative to the focal point; a real image would appear on a screen and is inverted.
• Convex Mirrors: Create only virtual images, which are upright, diminished in size, and located between the mirror and the focal point. The image is always located behind the mirror.

Dispersion

• Light is made of different colours. Different colours of light have different wavelengths.
• When light travels through a prism or other transparent medium, different wavelengths of light are refracted at different angles.
• This separation of light into its constituent colours is called dispersion.

Refraction

• Refraction is the bending of light as it passes from one medium to another. This is governed by Snell's law, which relates the angles of incidence and refraction to the refractive indices of the two media.
• Different materials have different refractive indices.