cathode: When two metal plates are placed facing each other (i.e. parallel plates -- see capacitor) in an electrical circuit the negatively charged plate is called the cathode (the positively charged plate is called the anode).

cathode rays: When a cathode is heated with the application of a large voltage a beam flows from the cathode toward the anode. J.J. Thompson realized that the ray consisted of particles (rather than light as was presumed) and named them electrons. This effect was one of the clues that classical physics was incomplete, heralding the birth of quantum mechanics. (For more information, see the off-site explanation)

charge: (n.) That property of matter which allows the matter to interact via one of the fundamental forces (see interaction). The word "charge" is generally used to denote electrical charge, but it may also refer to gravitational charge (usually called mass), to weak charge, or to color charge. (v.) As a verb, this also denotes the building up of (typically electrical) charge.

charge, color:

charge, electrical: That property of matter which allows the matter to interact via the electrical interaction. (Electrical charge is expressed in units of coulmb which were named for Charles A. Coulmb.) The electrical charge can be either positive or negative such that like charges repel and opposite charges attract. The electrical charge of some common particles are:
electron (q_e = -1.60 x 10^-19 Coulombs)
proton (q_p = +1.60 x 10^-19 Coulombs)
neutron (q_n = 0.00 Coulombs)
quarks (depending on the type, either ¹/₃(q_e) or ²/₃(-q_e) )

charge, gravitational:

charge, weak:

charge carrier: This term refers to the availability of electrons for carrying the electrical current. (See also positive charge carriers [aka holes] and negative charge carriers)

charge carrier, negative: A negative charge carrier is an electron which is in the conduction band, the flow of which explicitly creates the electrical current. (See also positive charge carriers)

charge carrier, positive: A positive charge carrier is a hole which "gets filled" by electrons. As an electron flows to the right to fill a hole, it leaves a hole behind on the left; in effect the hole has "moved" to the left because the electron has moved to the right. The flow of these holes are explicitly the cause of the electrical current. (See also negative charge carriers)

circuit: The route laid out with wires which connect circuit components along which the electrical current flows. As one follows the electrons around the circuit, the electrical potential increases, but the current does not diminish. This is equivolent to saying that the charges are not used up, but the electrical potential energy is. However, as with water flowing through a pipe, it is possible to split the current amoung a variety of paths. Circuit analysis is usually concerned with the values of the current through the components and voltages between points along the circuit, such as across the components.

circuit component: Those items which make an electrical circuit do more than simply direct the flow of charge. Some examples of circuit components are capacitors, diodes, inductors, and resistors. Generally, the components are modeled as ideal, for which a graph of voltage versus current has a characteristic shape. This is useful for predicting what happens when several components are added to a circuit and realistic if the component is used in a specific region of values of voltage and current.

classical:

commute:

component:

conduct: The conduction of electricity refers to the process of electrical charge flowing through a material. The conduction of the charge carriers is the electrical current.

conductor: A material which has a small energy gap is a conducting material. A conductor conducts electricity very well; it conducts better than either an insulator or a semi-conductor.

continuum:

coordinate system: In order to describe where things are, one needs to lay out the basic directions (equivolent to North, South, East, and West on a map). This is a coordinate system. There are two main differences between the directions on a map and in a coordinate system: First, a coordinate system has an origin --- a place from which every other place is referenced; the map-equivolent would be if everything were measured from city hall - "The bank is three blocks south of city hall." "The grocery store is two block east and one block north of city hall." etc. Second, a mathematical coordinate system would treat the north-south pair as a single dimension. One would be the "positive direction" and the other would be the "negative direction." (It is arbitrary which is which, but there is usually a convention.) i.e. if we call north the "positive North-South direction," then south is the negative North-South direction." Similarly, if east is the "positive East-West direction," then west is the "negative East-West direction." Finally, it is important in mathematics that the dimensions of a coordinate system be perpendicular. (North-South is perpendicular to East-West.)

coulomb force: (see force, electromagnetic interaction)

current, electrical: The flow (usually, the motion through a wire) of electrical charge (referred to as charge carriers). While current is simply the flow of charge, in general, people also refer to AC and DC. Any moving charge is a current; there are a variety of convenient ways to move a charge. AC (alternating current) is what comes from the outlets in your house. This is where the electrical charges oscillate back and forth rather than flow throughout the wires. DC (direct current) is what comes from batteries; this is where the electrical charges flow through the wire from one battery terminal to the other battery terminal. (Notice that the notion "AC current" is redundant, because "AC current" means "Alternating Current current"!) Although in a wire, it is a flow of electrons which causes the current, technically, the current is the flow of positive charge. It can be shown that positive charge moving to the right has the same effect as negative charge moving to the left. Both of these describe a current to the right. (See charge carriers, positive for a description.) Electrical current is expressed in units of ampere which were named for Andre Marie Ampere.