Light Revision

A comprehensive vocabulary review of foundational light concepts, including light propagation, reflection, periscopes, lateral inversion, refraction, dispersion, primary colours, lenses, ray diagrams, and eye anatomy.

Speed of Light

The rapid rate at which light travels, measuring approximately $300{,}000\,\text{kilometres per second}$, which allows light to travel from the Earth to the moon in $1.28\,\text{s}$.

Light Source

An object that produces and gives off its own light energy, such as a burning match.

Light Reflector

An object that gives off light by reflecting it rather than generating its own; for example, a red rose reflects red light while absorbing all other colours of white light.

Law of Reflection

A fundamental optical rule stating that the angle of incidence is equal to the angle of reflection relative to the normal line on a plane mirror.

Periscope

An optical device that uses multiple angled mirrors (such as Mirror A and Mirror B) to reflect light paths and allow an observer to view objects around barriers or out of direct line of sight.

Lateral Inversion

The optical effect produced by plane mirrors where images are reversed horizontally from left to right (such as the reversed lettering printed on the front of an ambulance).

Refraction

The bending or change in direction of light as it travels across the boundary from one medium into another of differing optical density.

Refraction Rules of Direction

When light travels from a less dense medium to a more dense medium, it bends towards the normal; when it travels from a more dense medium to a less dense medium, it bends away from the normal.

Virtual Image from Refraction

An apparent image formed because light bending away from the normal as it leaves water causes the brain, which assumes light travels in straight lines, to perceive an underwater object (such as a fish) as being closer to the surface than its actual position.

Dispersion

The separation of white light into its constituent visible spectrum colours (such as red, green, and blue) by passing it through a triangular prism.

Primary Colours of Light

Red, green, and blue (RGB), which can be combined to produce any other colour and satisfy the relationship $\text{R} + \text{G} + \text{B} = \text{White}$.

White Object Reflection

The property of an object appearing white because it reflects all wavelengths and colours of light that shine upon it.

Converging and Diverging Lenses

A convex (converging) lens directs parallel incoming rays inward to cross at a focal point ($F$), whereas a concave (diverging) lens refracts parallel incoming rays outward so they appear to emanate from a focal point ($F$).

Convex Lens Ray Diagram Rules

A two-step ray construction method: 1) Draw a ray parallel to the principal axis that refracts through the focal point ($f$) on the opposite side; 2) Draw a ray through the pole of the lens that continues straight through without changing direction.

Anatomy of the Human Eye

The structural components involved in vision, which include the cornea, pupil, iris, lens, vitreous gel, retina, macula, fovea, and optic nerve.