the ability of the eye to adjust its focal length is known as accommodation


The size of the wave. For a physical wave like a water wave, this will be the actual height in meters. For a sound wave (a pressure wave in the air) this will be in units of pressure Pa.

analytical methods

the method of determining the magnitude and direction of a resultant vector using the Pythagorean theorem and trigonometric identities


For each type of particle in the universe, there is an antimatter counterpart. These antimatter counterparts have the same mass as the usual particles, but the sign of the electric charge is reversed: anti-electrons are positively charged, while anti-protons are negatively charged. When matter and antimatter are brought into contact, the result is their mutual destruction (or annihilation) into pure energy.


a device that stores electric charge

center (optics)

For a lens, where the lens is thickest.

For a mirror, the center is the center of curvature.


describes a time cycle about one day in length


refers to the interchangeability of order in a function; vector addition is commutative because the order in which vectors are added together does not affect the final sum


a piece of a vector that points in either the vertical or the horizontal direction; every 2-d vector can be expressed as a sum of two vertical and horizontal vector components

concave mirror

A mirror that bends towards the incoming light )


A set of weakly photosensitive, cone-shaped neurons in the fovea of the retina that detects bright light and is used in daytime color vision. There are cones responsible for red light, green light, and blue light.

converges (optics)

Bring light rays to a point.

converging (or convex) lens

a convex lens in which light rays that enter it parallel to its axis converge at a single point on the opposite side

convex mirror

A mirror that bends away from the light source (


The transparent layer over the front of the eye that helps focus light waves. Most of the focusing of the eye actually happens at the cornea, not in the lens.


An equation representing a common quantity. This equation does not elucidate a fundamental truth of the Universe, it just defines an idea. For example, velocity = distance / time. There are no fundamental truths here, that is just the definition of velocity.


the orientation of a vector in space

diverge (optics)

Spread the light rays apart.

diverging lens

a concave lens in which light rays that enter it parallel to its axis bend away (diverge) from its axis


From physics 131: The ability of an object to do work. I.e. its capability to exert a force for a distance. Whether that ability is realized is not relevant.

Energy comes, ultimately, in only two types: kinetic and potential. Kinetic energy is the capability to do work due to motion; thermal energy due to temperature, is at a fundamental level, kinetic energy due to molecular motion. Potential energy is the energy due to the relative positions of two objects: gravitational potential energy arises from the relative positions of an object and the Earth. "What is the gravitational potential energy of the ball?" is, technically, a meaningless question. The question only has relevance when considered in conjunction with the fact that the Earth exists.


When the image is the same orientation as the object

far point

The furthest an object can be from an eye and still be seen clearly.

focal length

distance from the center of a lens or curved mirror to its focal point

focal point

for a converging lens or mirror, the point at which converging light rays cross; for a diverging lens or mirror, the point from which diverging light rays appear to originate

fovea centralis

region in the center of the retina with a high density of photoreceptors and which is responsible for acute vision


The number of wave crests passing a point per second. The unit is 1/s or, equivalently, Hertz Hz.

The frequency will be 1 divided by the period T.

geometric optics

part of optics dealing with the ray aspect of light

head (or tip)

the end point of a vector; the location of the tip of the vector’s arrowhead; also referred to as the “tip”

head-to-tail method

a method of adding vectors in which the tail of each vector is placed at the head of the previous vector


The transfer of energy through microscopic collisions: fast moving (high-temperature) atoms colliding with slow moving (low-temperature) atoms results in the movement of energy from hot-to-cold.

Relevant to this course, the collisions could also be with photons.

hyperopia (also, farsightedness)

Visual defect in which the image focus falls behind the retina, thereby making images in the distance clear, but close-up images blurry.


The apparent reproduction of an object, formed by an optical element (or collection of them) reflecting and/or refracting light.

image distance

the distance of the image from the center of a lens

incident ray

Incoming ray

index of refraction

for a material, the ratio of the speed of light in vacuum to that in the material [latex] n = c/v [/latex]. Always greater than 1.


Power per area:

I = P/A

or, using P = E/t,

I = E/(At)


When the image is upside-down with respect to the object.

ionizing radiation

radiation that ionizes materials that absorb it


The pigmented, circular muscle at the front of the eye that regulates the amount of light entering the eye.

Law of Reflection

The angle of reflection equals the angle of incidence.

Law of Refraction (Snell's Law)

n_1 sin (theta_1) = n_2 sin (theta_2)

lens (eye)

The transparent, convex structure behind the cornea that helps focus light waves on the retina. The lens is for the fine-tuning.


ratio of image height to object height


the length or size of a vector; magnitude is a scalar quantity


Metaphysics is the branch of philosophy that examines the fundamental nature of reality, including the relationship[1] between mind and matter, between substance and attribute, and between potentiality and actuality.[2] The word "metaphysics" comes from two Greek words that, together, literally mean "after or behind or among [the study of] the natural" -Wikipedia


A smooth surface that reflects light at specific angles, forming an image of the person or object in front of it

myopia (also, nearsightedness)

Visual defect in which the image focus falls in front of the retina, thereby making images in the distance blurry, but close-up images clear

near point

The closest an object can be to the eye and still be seen clearly.

object distance

the distance of an object from the center of a lens


Ontology is the philosophical study of being. More broadly, it studies concepts that directly relate to being, in particular becoming, existence, reality, as well as the basic categories of being and their relations. Traditionally listed as a part of the major branch of philosophy known as metaphysics, ontology often deals with questions concerning what entities exist or may be said to exist and how such entities may be grouped, related within a hierarchy, and subdivided according to similarities and differences. -Wikipedia

optical axis

an imaginary line that passes through the optical element in a way that's perpendicular to it

optical element

A lens or a mirror


The simplest conception is a ball. Particles have a fixed position and speed. Particles are characterized, by their energy, momentum, and how many of them there are.


Particles of light. For a given frequency [latex] \nu [/latex], the smallest amount of energy that you can have is one photon's worth: [latex] E_\gamma = h \nu [/latex].

pi bond

a type of covalent bond that results from the side-by-side overlap of two p orbitals


The energy or work per time. The unit is the J/s or the Watt (W)

power (optics)

inverse of focal length


Visual defect in which the image focus falls behind the retina, thereby making images in the distance clear, but close-up images blurry; caused by age-based changes in the lens.


A fundamental relationship that describes how the Universe works. These are the fundamental truths of Nature. When writing a principle as an equation, the "=" is translated as "causes." For example, Newton's 2nd Law, F = ma, a force F causes an object m to accelerate (change its speed or direction) a. These principles are where we begin our analyses.


The small opening at the front of the eye though which light enters. Appears black (or red in flash photographs!). The size is controlled by the iris.


straight line that originates at some point

real image

image that can be projected

refracted ray

A ray that has been bent by a refraction, such as in a lens.


changing of a light ray’s direction when it passes through variations in matter


the sum of two or more vectors

resultant vector

the vector sum of two or more vectors


layer of photoreceptive and supporting cells on the inner surface of the back of the eye


main photopigment in vertebrates


Strongly photosensitive, achromatic, cylindrical neuron in the outer edges of the retina that detects dim light and is used in peripheral and nighttime vision. Can only see in black and white.


a quantity with magnitude but no direction

sigma bond

a covalent bond in which the electron density is concentrated in the region along the internuclear axis; that is, a line between the nuclei would pass through the center of the overlap region. Single bonds in Lewis structures are described as σ bonds in valence bond theory.

superior colliculus

paired structure in the top of the midbrain, which manages eye movements and auditory integration

suprachiasmatic nucleus

cluster of cells in the hypothalamus that plays a role in the circadian cycle


the start point of a vector; opposite to the head or tip of the arrow

thin lens

a lens whose thickness allows rays to refract but does not allow properties such as dispersion and aberrations.

tonic activity

in a neuron, slight continuous activity while at rest

valence bond theory

Describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single electron) that yield a pair of electrons shared between the two bonded atoms.


a quantity that has both magnitude and direction; an arrow used to represent quantities with both magnitude and direction


The point where the optical axis meets the optical element.

vertex (optics)

The point where the optical axis meets the optical element

virtual image

image that cannot be projected


sense of sight

wave-particle duality

A description for the fundamentally new nature of very small objects like electrons and photons: sometimes they behave like waves and sometimes they behave like particles. Neither picture is 100% correct: electrons are neither waves nor particles, but have properties of both.

In fact, all objects exhibit wave particle duality. You have a wavelength! However, your wavelength is too small to notice (check with de Broglie if you want). The effect is really only noticeable for small objects.


The distance from one point in a wave to the same point on the next wave: for example, crest-to-crest. This is a distance measured in meters.


The exchange of energy through the application of a force through some distance.


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Physics 132: What is an Electron? What is Light? by Roger Hinrichs, Paul Peter Urone, Paul Flowers, Edward J. Neth, William R. Robinson, Klaus Theopold, Richard Langley, Julianne Zedalis, John Eggebrecht, and E.F. Redish is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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