Introduction to Light and Optics

Comprehensive vocabulary terms and definitions covering the properties of light, production methods, reflection, refraction, and lens terminology based on the lecture notes.

Light

An electromagnetic wave that travels in straight lines at a very high speed and does not require a medium to travel.

James Clerk Maxwell

The scientist who proposed that light is a type of electromagnetic radiation given off by the Sun.

Luminous

Objects that produce their own light, such as the Sun.

Non-Luminous

Objects that do NOT produce their own light and can only be seen if light is reflected off of them, such as a tree.

Incandescence

The production of light by extremely high temperatures; any object that gets hotter and hotter will eventually produce light.

Electric Discharge

The process of creating light by passing an electric current through a gas, such as lightning.

Phosphorescence

The process of producing light by the absorption of UV light, creating the emission of visible light over an extended period of time (e.g., glow in the dark).

Fluorescence

The immediate emission of visible light as a result of the absorption of UV light, such as in a fluorescent light bulb.

Chemiluminescence

The direct production of light caused by a chemical reaction with little to no heat produced, such as glow sticks.

Bioluminescence

The production of light from a living organism caused by a chemical reaction with little to no heat produced, such as fireflies.

Triboluminescence

The production of light from friction as a result of scratching, crushing, or rubbing certain crystals.

Light Emitting Diode (LED)

An electronic device that allows an electric current to flow only in one direction using a semiconductor; it is the most energy-efficient light source.

Light Ray

A line and arrow representing the direction and straight-line path of light.

Geometric Optics

The use of light rays to determine the path of light when it strikes an object.

Incident Light

Light that strikes an object.

Transparent

A material that allows light to pass right through it.

Translucent

A material that allows some light to pass through it.

Opaque

A material that allows no light to pass through it.

Image

The reproduction of an original object produced by light.

Mirror

A polished surface that exhibits reflection, consisting of a front sheet of glass and a thin layer of reflective silver or aluminum.

Reflection

The bounce back of light from a surface.

Plane Mirror

A flat mirror.

Angle of Incidence

The angle between the incident ray and the normal.

Angle of Reflection

The angle between the reflected ray and the normal.

Laws of Reflection

1. The angle of incidence equals the angle of reflection. 2. The incident ray, reflected ray, and normal all lie in the same plane.

Specular Reflection

Reflection off a smooth, shiny surface where parallel rays have identical angles of incidence.

Diffuse Reflection

Reflection off an irregular or dull surface where parallel incident rays have different angles of reflection.

Virtual Image

An image where light does not actually arrive at or come from the image location.

SALT

An acronym for describing images in a plane mirror: Size (same size), Attitude (upright), Location (behind mirror), and Type (virtual).

Concave Mirror

A converging mirror that curves inward.

Convex Mirror

A diverging mirror that curves outward.

Centre of Curvature ($C$)

The centre of the sphere from which the mirror comes.

Principal Axis

The straight line passing through the Centre of Curvature ($C$) and the vertex of the mirror.

Vertex ($V$)

The point where the principal axis touches the mirror.

Focus ($F$)

The point where parallel rays meet (in concave mirrors) or appear to meet (vertically behind convex mirrors); it is located halfway between $C$ and the mirror.

Refraction

The bending or change in direction of light when it travels from one medium into another.

Speed of Light in a Vacuum

$3.00 \times 10^{8}\,\text{m/s}$.

Angle of Refraction

The angle between the refracted ray and the normal.

Bending Toward Normal

Occurs when light travels from a less dense medium to a denser medium (e.g., Air to Water), causing it to slow down.

Bending Away From Normal

Occurs when light travels from a more dense medium to a less dense medium, causing its speed to increase.

Critical Angle

The angle of incidence at which the angle of refraction becomes $90^{\circ}$.

Total Internal Reflection

Occurs when the angle of incidence is increased beyond the critical angle, causing the refracted ray to reflect back into the medium.

Converging Lens

Also known as a convex lens, it is thickest at the centre and causes light rays to converge to a single point.

Diverging Lens

Also known as a concave lens, it is thinnest at the centre and causes light rays to spread out after refraction.

Optical Centre ($O$)

The centre of a lens where light rays pass through without refracting.

Principal Focus ($F$)

In a lens, the point where light rays that are parallel to the principal axis converge after refraction.

Secondary Principal Focus ($F'$)

The focus on the same side of the lens as the incident rays for a converging lens.

Index of Refraction ($n$)

The ratio of the speed of light in a vacuum ($c$) to the speed of light in a certain medium ($v$), represented by the formula $n = \frac{c}{v}$.

Snell's Law (General)

A formula that works with any two mediums: $n_{R} \times \sin(\theta_{R}) = n_{I} \times \sin(\theta_{I})$.

Emergent Ray

The ray leaving the lens after refraction.

Myopia

nearsightedness

Image forms in front of the retina

Corrected with a concave / diverging lens

Hyperopia

Farsightedness

Image forms behind the retina

Corrected with a convex or converging lens

Presbyopia

Farsightedness

Age related difficulty focusing on nearby objects

caused by the lens becoming less flexible over time

Corrected with reading glasses convex or converging lens