Power Point Chapter 3 Electricity Flashcards by Angel Godsell

oSmallest unit of positive charge
oLocked in the nucleus by very strong forces

•Protons

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oSmallest unit of negative charge
oFree to move between orbitals and atoms
o“Free electrons” are those not associated with a nucleus

•Electrons

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Electricity concerns the DISTRIBUTION and MOVEMENT of ELECTRONS and has LITTLE to do with the?

positively charged protons locked within the atomic nucleus.

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(electron) (resting/lacking movement)

•Electro statics

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(electrons) at rest

•Electric charges

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•Electrification – process of electron charges being?

added to or subtracted from an object.
oNegative and positive

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Relative terms – not positive (protons), just?

less negative (fewer electrons). Nearly all objects have negative charges.

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•Earth serves as infinite reservoir of pos and neg charges in equal distribution
•Has no potential to perform work/release energy (symbol on pg 37)

oZero or ground potential

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oLike charges repel
oUnlike charges attract
oFigure 3-1, pg 37

•Repulsion–attraction

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oForce between two charges is directly proportional to product of their magnitudes and inversely proportional to square of distance between them
oFormula on pg 37

•Inverse square law

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oCharges reside on external surface of solid conductors

•Distribution

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oAttempt to repel each other due to negative charges

•Distribution

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oCharges reside equally throughout nonconductors

•Distribution

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oGreatest concentration of charges will gather at sharpest area of curvature

•Concentration

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oOn a cylindrical wire, charges are equidistant from each other

•Concentration

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oInterior components of x-ray tubes are rounded and highly polished to eliminate sharply curved surfaces

•Concentration

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oOnly negative charges move along solid conductors
oCharges move along surface of solid conductor

•Movement

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oAbrasion of two conductive materials creates a transfer of charges between the materials

•Friction

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•Occurs when one object is rubbed on another
oFor example, rubbing balloon on wool sweater, combing hair during winter

•Friction

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oPhysically touching a charged body to a neutral body, creates a transfer of charge

•Contact

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•Occurs when two objects touch
oPermits electrons to move from one object to another
oFor example, walking across floor (electrification by friction) and touching doorknob (electrification by contact)

•Contact

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•Static discharge
oReleases excess energy as light photons

Contact

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oBring a charged body in close proximity to a neutral object, without physical contact, creates a charge in the neutral object

•Induction

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•Used in operation of electronic devices

•Induction

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•Process of electric fields acting on one another without physical contact

•Induction

(electrons) (moving, motion)

Electro dynamic

oNegative to positive (less negative) Movement of?

Electrons

electrons moving in predominantly the same direction

Electric current

space from which air has been removed. Few atoms oppose electron flow and permit electrons to reach the speed to produce x-rays (x-ray tube)

Vacuum

Properties of conducting materials –

Princ, pg 41, Table 3-1

pathway (usually copper wire) that permits electrons to move in a complete circle from their source, through resistors and back to the source.

Electrical circuit

An electrical circuit must have an excess charge at one end and?

comparative deficiency at the other to allow electrons to flow

• Excess electron sources-

a.Battery – converts chemical energy to electrical energy b.Generator – converts mechanical energy to electrical energy c.Solar converter – converts solar photons to electrical energy d.Atomic reactor – converts nuclear energy to electrical energy

converts chemical energy to electrical energy

a.Battery –

converts mechanical energy to electrical energy

b.Generator –

converts solar photons to electrical energy

c.Solar converter –

converts nuclear energy to electrical energy

d.Atomic reactor –

Electrons move from areas of high (neg) to low (pos or less neg) concentration, Electron flow is from

negative to positive

oFrom positive to negative oDue to movement of “electron holes” which is opposite to electron movement

Conventional current flow

oQuantity or number of electrons flowing

Current

oUnit of current is the ampere aka amp

Current

oSymbolized by the letter A

Current

oConsists of the movement of 6.24 x 10 18th electrons per second past a given point – one coulomb of electrical charge flowing per second

Current

o1 ampere = 1 coulomb/1 second

Current

X-ray equip uses milliamperage to regulate the number of electrons available to produce x-ray photons

Current

Current = Quantity (#) of

electrons flowing

oUnit of current o1 C/sec oCurrent in x-ray machines expressed in milliamperes (mA)

•ampere

oForce with which electrons travel

Potential Difference

oExpressed as voltage; represented by V; volt is 1 joule (J) of work done on 1 coulomb of charge; 1 volt = 1 joule/1 coulomb

Potential difference

oDependent on the difference between the number of excess electrons at one end of the circuit and the deficiency at the other end

Potential difference

oDoes not have to be an actual flow of current for the difference to exist

Potential difference

oTherefore termed potential difference

Potential difference

oAKA electromotive force (emf) - the max diff of potential between pos and neg end of the electron source

Potential difference

•Force that drives electrons

Potential difference

•Electromotive force (E M F)

Potential difference

•Voltage oE M F used to do work

Potential difference

•Area of higher and lower concentration of electrons oUnequal forces try to balance

Potential difference

Impedance or resistance

Resistance

Opposition to current flow in the circuit

Resistance

Unit of resistance is the ohm; represented by the symbol Ω (omega)

Resistance

Direction of travel: Alternating current/direct current

(A C/D C) -Resistance

when electrons move first in one direction and then reverse and move in the opposite direction; AC resistance is measured as admittance

AC -Resistance

when all electrons move in the same direction; DC resistance is measured as conductance

DC -Resistance

unit for admittance and conductance

Siemens (S)

Amount of opposition to current

Resistance

Measured in ohms

Resistance

•Resistance terms based upon current type

oConductance (D C) oAdmittance (A C)

Resistance is Dependent upon four things:

oMaterial’s conductivity oLength oDiameter oTemperature

Dependent on configuration of atom’s:

Material’s Conductivity

the outermost & sometimes next to outermost orbital shell

Valence band

beyond the valance band, not an orbital shell, but within the force field of the atom

Conduction band –

Valence band and conduction band overlap

•Conductors

oValence band and conduction band in close proximity

•Semi-conductors

Valence band and conduction band overlap greatly

Superconductors

oValence band and conduction band far apart

Insulators

Length is ______ related to Resistance.

Directly

As length of solid conductor increases, resistance increases proportionally; ex –?

length doubles, resistance doubles Directly related to resistance

oEfficient circuit designs minimize circuit pathways and?

length Directly related to resistance

Electricians wire buildings using the shortest run possible, to lessen total?

resistance

Diameter is ______ related to resistance.

Inversely

As cross-sectional diameter of solid conductor increases, resistance decreases; ex –?

diameter doubles, resistance halved Inversely related to resistance

oThicker wires offer less?

Resistance

oExpressed in wire gauge •14g, 16g, 18g, 22g, etc. •Lower number = ______ ______

thicker wire

Temperature is ______ related to resistance.

Directly

Increased atomic motion due to increased temperature prevents electrons from flowing freely; ex –?

higher temp, more resistance Directly related to resistance

Electronics engineers go to great lengths to minimize _____ ____ _____.

circuit heat build-up

Ohm’s Law – mathematical relationship between _______, _______ ______, and _________.

current, potential difference, and resistance

V = potential difference

(volts)

I = current

(amperes)

R = resistance

(ohms)

Power Formula – used to calculate the total amount of _____ used in an electric circuit.

power

P = power

Watts (unit of power)

P = power

Watts (unit of power)

Watt is defined as 1 _____ flowing through 1 _____.

Ampere - Volt

I = current

Amperes (unit of current)

V = potential difference

Volts (unit of potential difference)

Calculation of Ohm’s Law varies depending upon ______ ______.

circuit type

Current flow is divided between branches of circuit

Parallel Circuits

As more ______ are added to a parallel circuit, total resistance drops, total amperage increases, and total voltage remains unchanged.

resistances

Adding resistances in a parallel circuit, increases ________ ________.

circuit temperatures

variable resistor used to control current, not practical for high voltage situations

Rheostat

Devices added to circuits for protection from extreme overheating

Circuit Breaker and Fuse

pops open and can be reset once the cause of the problem has been located and removed from the circuit

oCircuit breaker

constructed with a metal tab that will melt when dangerously heated, breaking the circuit. Not reusable, must be replaced

oFuse

It consists of the movement of 6.24 x 10^18 electrons per second past a given point:

Ampere (1 ampere = 1 coulomb/1 second).

Properties of Conducting Materials

Insulator Semiconductor Conductor Superconductor

Material: Plastic, Rubber, Glass

Insulator

Material: Silicon, Germanium

Semiconductor

Material: Copper, Aluminum

Conductor

Material: Titanium

Superconductor

Greatly overlapping conduction and valence bands; conducts with little or no electrical potential; most current systems require extreme cold to function although research indicates room-temperature superconductors may be developed soon.

Superconductor

Overlapping conduction and valence bands; conducts with minor resistance, varying denendina on temperature and other conditions.

Conductor

Small energy difference between conduction and valence bands; conducts or resists, depending on temperature and other conditions.

Semiconductor

Large energy difference between conduction and valence bands; resists electron flow.

Insulator