physics exam 2 (ch 5,7-10)

equipotential line

2D representation of an equipotential surface

coulomb's law

F12 (r) = k x (q1 q2) / r12^2

ampere (amp)

SI unit for current; 1A=1C/s

SQUID

Superconducting Quantum Interference Device device that is a very sensitive magnetometer, used to measure extremely subtle magnetic fields

permittivity of vacuum

aka Permittivity of free space; constant describing the strength of the electric force in a vacuum

loop rule

algebraic sum of changes in potential around any closed circuit path (loop) must be zero

electrostatic force

amount and direction of attraction or repulsion between two charged bodies; the assumption is that the source charges remain motionless

linear charge density

amount of charge in an element of a charge distribution that is essentially one-dimensional (width and height are much much smaller than length); its units are C/m

volume charge density

amount of charge in an element of a three-dimensional charge distribution; its units are C/m^3

surface charge density

amount of charge in an element of a two-dimensional charge distribution (thickness is small); its units are C/m^2

capacitance

amount of charge stored per unit volt

internal resistance

amount of resistance to the flow of current within the voltage source

static electricity

buildup of electric charge on the surface of an object; the arrangement of the charge remains constant ("static")

voltage

change in potential energy of a charge moved from one point to another, divided by the charge; units of potential difference are J/C --> volt

induced surface charges

charges that occur on a dielectric surface due to its polarization

RD circuit

circuit that contains both a resistor and a capacitor

circuit

complete path that an electrical current travels along

series combination

components in a circuit arranged in a row one after the other in a circuit

parallel combination

components in a circuit arranged with one side of each component connected to one side of the circuit and the other sides of the components connected to the other side of the circuit

superposition

concept that states that the net electric field of multiple source charges is the vector sum of the field of each source charge calculated individually

dielectric strength

critical electrical field strength above which molecules in insulator begin to break down and the insulator starts to conduct

conventional current

current that flows through a circuit from the positive terminal of a battery through the circuit to the negative terminal of the battery

capacitor

device that stores electrical charge and electrical energy

potential difference

difference in electric potential between two points in an electric circuit, measured in volts

induced electric-dipole moment

dipole moment that a nonpolar molecule may acquire when it is placed in an electrical field

xerography

dry copying process based on electrostatics

resistance

electric property that impedes current; for ohmic materials, it is the ratio of voltage to current R = V/I

induced electrical field

electrical field in the dielectric due to the presence of induced charges

conduction electron

electron that is free to move away from its atomic orbit

ohm's law

empirical relation stating that the current I is proportional to the potential difference V; it is often written as V = IR, where R is the resistnace

electron-volt

energy given to a fundamental charge accelerated through a potential difference of one volt

electromotive force (emf)

energy produced per unit charge, drawn from a source that produces an electrical current

energy density

energy stored in a capacitor divided by the volume between the plates

dielectric constant

factor by which capacitance increases when a dielectric is inserted between the plates of a capacitor

electrostatic precipitators

filters that apply charges to particle in the air, then attract those charges to a filter, removing them from the airstream

infinite plane

flat sheet in which the dimensions making up the area are much, much greater than its thickness, and also much, much greater than the distance at which the field is to be calculated; its field is constant

current density

flow of charge through a cross-sectional area divided by the area

schematic

graphical representation of a circuit using standardized symbols for components and solid lines for the wire connecting the components

shock hazard

hazard in which an electric current passes through a person

thermal hazard

hazard in which an excessive electric current causes undesired thermal effects

ammeter

instrument that measures current

dielectric

insulating material used to fill the space between two plates

resistivity

intrinsic property of a material, independent of its shape or size, directly proportional to the resistance, denoted by p

Josephson junction

junction of two pieces of superconducting material separated by a thin layer of insulating material, which can carry a supercurrent

potential drop

loss of electric potential energy as a current travels across a resistor, wire, or other component

Van de Graaff generator

machine that produces a large amount of excess charge, used for experiments with high voltage

conductor

material that allows electrons to move separately from their atomic orbits; object with properties that allow charges to move about freely within it

insulator

material that holds electrons securely within their atomic orbits

electrical conductivity

measure of a material's ability to conduct or transmit electricity

law of conservation of charge

net electric charge of a closed system is constant

electric force

noncontact force observed between electrically charged objects

diode

nonohmic circuit device that allows current flow in only one direction

field line density

number of field lines per square meter passing through an imaginary area; its purpose is to indicate the field strength at different points in space

ohm

omega; unit of electrical resistance omega = 1V / A

electrostatic repulsion

phenomenon of two objects with like charges repelling each other

electrostatic attraction

phenomenon of two objects with opposite charges attracting each other

Meissner effect

phenomenon that occurs in a superconducting material where all magnetic fields are expelled

superconductivity

phenomenon that occurs in some materials where the resistance goes to exactly zero and all magnetic fields are expelled, which occurs dramatically at some low critical temp (Tc)

dielectric breakdown

phenomenon that occurs when an insulator becomes a conductor in a strong electrical field

electric field

physical phenomenon created by a charge; it transmits a force between two charges

electric charge

physical property of an object that causes it to be attracted toward or repelled from another charged object; each charged object generated and is influenced by a force called an electric force

terminal voltage

potential difference measured across the terminals of a source when there is no load attached

electric potential

potential energy per unit charge

electric potential energy

potential energy stored in a system of charged objects due to the charges

charging by induction

process by which an electrically charged object brought near a neutral object creates a separation in that object

grounding

process of attaching a conductor to the earth to ensure that there is no potential difference between it and Earth

dipole moment

property of a dipole; it characterizes the combination of distance between the opposite charges, and the magnitude of the charges

electric dipole moment

quantity defined as P = qd for all dipoles, where the vector points from the negative to positive charge

electrical current

rate at which charge flows I = dQ/dt

equivalent resistance

resistance of a combination of resistors; it can be thought of as the resistance of a single resistor that can replace a combination of resistors in a series and/or parallel circuit

Kirchhoff's rules

set of two rules governing current and changes in potential in an electric circuit

polarization

slight shifting of positive and negative charges to opposite sides of an object

ink jet printer

small ink droplets sprayed with an electric charge are controlled by electrostatic plates to create images on paper

field line

smooth, usually curved line that indicates the direction of the electric field

infinite straight wire

straight wire whose length is much, much greater than either of its other dimensions, and also much, much greater than the distance at which the field is to be calculated

photoconductor

substance that is an insulator until it is exposed to light, when it becomes a conductor

junction rule

sum of all currents entering a junction must equal the sum of all currents leaving the junction

equipotential surface

surface (usually in 3D) on which all points are at the same potential

electric dipole

system of 2 equal but opposite charges a fixed distance apart

parallel-plate capacitor

system of two identical parallel conducting plates separated by a distance

critical temperature

temp at which a material reaches superconductivity

electric potential difference

the change in potential energy of a charge q moved between two points, divided by the charge

electrical power

time rate of change of energy in an electric circuit

continuous charge distribution

total source charge composed of so large a number of elementary charges that it must be treated as continuous, rather than discrete

dipole

two equal and opposite charges that are fixed close to each other

nonohmic

type of a material for which Ohm's law is not valid

ohmic

type of a material for which Ohm's law is valid -> the voltage drop across the device is equal to the current times the resistance

permanent dipole

typically a molecule; a dipole created by the arrangement of the charged particles from which the dipole is created

induced dipole

typically an atom, or a spherically symmetric molecule; a dipole created due to opposite forces displacing the positive and negative charges

principle of superposition

useful fact that we can simply add up all of the forces due to charges acting on an object

drift velocity

velocity of a charge as it moves nearly randomly through a conductor, experiencing multiple collisions, averaged over a length of a conductor, whose magnitude is the length of conductor traveled divided by the time it takes for the charges to travel the length

three-wire system

wiring system used at present for safety reasons, with live, neutral, and ground wires