Light & Optics

Light

An electromagnetic wave that travels in straight lines; a form of energy

Medium

Any physical substance through which energy can be transferred

Radiation

A method of energy transfer that does not require a medium, the energy travels at the speed of light

Electromagnetic Wave

a wave that has both electric and magnetic parts, does not require a medium, and travels at the speed of light

Visible Light

Electromagnetic waves that are visible to the human eye

Electromagnetic Spectrum

The classification of electromagnetic waves by energy

Visible Spectrum

The continuous sequence of colours that make up white light

Luminous

An object that emmits light

Non-Luminous

An object that reflects light and does not produce it

Incandescence

Light produced from heat

Electrical Discharge

Producing light by passing an electric current through a gas

Phosphorescence

An object absorbs UV light and emmits it slowly

Flourescence

An object absorbs UV light and refelcts it immediately

Chemiluminescence

The emission of light without heat from a chemical reaction

Bioluminescence

The production of light by means of a chemical reaction in an organism

Tribioluminescence

Producing light through scraping crystals together

LED (Light-Emitting Diode)

Light produced when a current runs through a semi-conductor

Laser

Emits a focused beam of one wavelength of light

Reflection

The bouncing back of light when it hits a surface it cannot pass through

First Law of Reflection

The angle of incident is equal to the angle of reflection

Second Law of Reflection

The incident ray, the normal, and the reflected ray lie in the same plane

Incident Ray

The ray that comes from an object and strikes a surface

Reflected Ray

The ray that is reflected off of a surface

Angle of Incidence

The angle between the incident ray and the normal (θi)

Angle of Reflection

The angle between the reflected ray and the normal (θr)

Plane Mirror

A mirror with a flat surface

SALT of a Plane Mirror

Same, Upright, Behind Mirror, Virtual

Concave Mirror

A mirror with a surface that curves inward

Principle Axis

The line passing through the centre of curvature and the vertex

Centre of Curvature

The centre of the sphere from which the mirror is made.

Vertex

The point in the middle of a mirror where the principle axis meets the mirror

Focus

The point at which parallel lines converge after reflecting off a concave mirror

SALT for a Concave Mirror (Beyond C)

Smaller, Inverted, Between F & C, Real

SALT for a Concave Mirror (Between C & F)

Bigger, Inverted, Beyond C, Real

SALT for a Concave Mirror (At C)

Same Size, Inverted, At C, Real

SALT for a Concave Mirror (At F)

No Image

SALT for a Concave Mirror (In Fron of F)

Bigger, Upright, Behind Mirror, Virtual

Incident ray parallel to the principle axis...

...reflects through the focus

Incident ray passing through the focus...

...reflects parallel to the principle axis

Incident ray passing through C...

...reflects back on itself

Incident rays striking the vertex...

...reflect at an equal angle with the principle axis

Convex Mirror

A mirror with a surface that curves outward

SALT for a Convex Mirror

Smaller, Upright, In Front of F, Virtual

Refraction

The bending or change in the speed and direction of light when in travels from one medium to another

Refracted Ray

The ray that is bent as it enters a new medium

Angle of Refraction

The angle between the refracted ray and the normal (θR)

Light bends _____ the normal when it enters a denser medium

Towards

Index of Refraction

The ratio of the speed of light in a vacuum to the speed of light in a medium

Light bends _____ the normal when it enters a less dense medium

Away from

Total Internal Reflection (TIR)

When light reflects at the barrier between two mediums instead of refracting

Critical Angle

The θi that results in the θR being exactly 90 degrees

Conditions for TIR

The first medium has a higher index and the θi is larger than the critical angle

Applications for TIR

Diamonds, fibre optic cables, prisms

Retro-Reflectors

An optical device in which the emergent ray is parallel to the incident ray

Lens

A transparent object with at least one curved side, causing light to refract

Converging Lens

A lens with a thick middle and thin edge, causes parallel rays to converge

Diverging Lens

A lens with a thin middle and thick edge, causes parallel rays to diverge

Secondary Focus

The focus on the opposite side of a lens’ image

2F/2F’

The point double the distance of the focal length

Converging lenses have _ F values

Positive

Diverging lenses have _ F values

Negative

Chromatic Aberration

Happens in thick lenses, different colours refract differently

SALT for a Converging Lens (Beyond 2F')

Smaller, Inverted, Between 2F and F, Real

SALT for a Converging Lens (At 2F')

Same Size, Inverted, At 2F, Real

SALT for a Converging Lens (Between 2F' and F’)

Larger, Inverted, Beyond 2F, Real

SALT for a Converging Lens (At F')

No Image

SALT for a Converging Lens (In Front of F')

Larger, Upright, Same Side, Virtual

SALT for a Diverging Lens

Smaller, Upright, Same Side/Closer to Lens, Virtual

Camera

Uses a converging lens to create a real image on a sensor

Focusing a Camera

Change the position of the lens to bring the image into focus

Zoom on a Camera

Adjust lenses to change the focal point

Movie Projector

Use a converging lens to magnify an image onto a big screen

Magnifying Glass

An object within the focus of a converging lens forms a magnifyed virtual image

Compound Microscope

Uses two converging lenses; objective lense creates a real image and the eyepiece lens creates a virtual image

Refracting Telescope

Like a microscope but the object is distant

Cornea

On the front of an eye; clear tissue that refracts light

Iris

The coloured part of the eye

Pupil

Where light enters the eye

Lens (eye)

Inside the eye, refracts light onto the retina

Cilliary Muscles

Open and close the iris to let more or less light into the eye

Vitreous Humour

Fluid in the middle of the eyeball

Aqueous Humour

Fluid in front of the lens

Retina

The area on the back of an eyeball where the image is formed

Optical Nerve

Takes the image to the brain

Rods

Sense monochromatic light

Cones

Sense coloured light

Myopia

Light focuses in front of the retina

Hyperopia

Light focuses behind the retina

Presbyopia

Caused by age; the lens cannot accomidate for nearby objects

Astygmatism

Incorrectly shped eyeball; only some light focuses