chapter 3 - Electricity Flashcards
Smallest unit of positive charge
Protons
Smallest unit of negative charge
Electrons
Free to move between orbitals and atoms
Electrons
What concerns the distribution and movement of electrons and has little to do with the positively charged protons locked within the atomic nucleus
Electricity
zero, neutral (so there wont be shock)
grounding
Electric charges at rest
Electrostatics
Repulsion
Attraction
Do like charges repel or attract
repel
Do unlike charges repel or attract
Attract
Force between two charges directly proportional to product of their magnitudes and inversely proportional to square of distance between them
Inverse square law
where is grounding located
secondary
-Charges reside on external surface of solid conductors
-attempt to repel each other due to negative charges
Distribution
where will the greatest concentration of chargers gather
they will gather at the sharpest area of curvature
Charges move along surface of solid conductor
Movement
What charges move along on solid conductor
Only negative
Abrasion of two conductive materials creates a transfer of charges between the materials
Friction
Physically touching a charged body to a neutral body, creates a transfer of charge
Contact
Bring a charged body in close proximity to a neutral object, without physical contact, creates a charge in the neutral object
Induction
how to electrons move
high to low concentration
Occurs when one object is rubbed on another
Friction
Occurs when two objects touch
Permits electrons to move from one object to another
contact
Releases excess energy as light photons
static discharge
Used in operation of electronic devices
Process of electric fields acting on one another without physical contact
Induction
Electrodynamics consist of :
Movement of electrons(negative to positive)
Electric current
Properties of conducting materials
Electrical circuit
Electron sources
what is the flow of electrons
negative to positive
cathode to anode
Conventional current flow
From positive to negative
Due to movement of “electron holes” which is opposite to electron movement
Quantity of electrons flowing
Current
Force with which they travel
Potential difference (expressed as voltage)
Direction of travel
Alternating current to Direct current (AC/DC)
opposition to current flow
Impedance or resistance
What is amperes
The current (how it is measured-unit)
Quantity of electrons flowing
amperes is the unit
Current
-Force that drives electrons
-Electromotive force (EMF)
-voltage
-area of higher to lower concentration of electrons
Potential Difference
What current does the xray tube only operate on
xray tube can only operate on direct current
what is needed to get direct current
Resistor
what is the symbol for resistor
black triangle
Resistance is dependent upon four things :
-materials conductivity
-length
-diamater
-temperature
-amount of opposition to current
-measured in ohms
- based upon current type
-conductance (DC)
- Admittance (AC)
Resistance
Valence band and conduction band overlap
Conductors
Valence band and conduction band in close proximity
Semi-conductors
valence band and conduction band overlap greatly
superconductors
valence band and conduction band far apart
Insulators
materials conductivity is dependents on configuration of atoms:
-valence band
-conduction band
individual photon
kev
kilovoltage peak
kvp
what is the relationship between length and resistance
directly related
why do electricians wire buildings using the shortest run possible ?
To lessen total resistance
as length of solid conductor increase, what happens to resistance
increases proportionally
what does the efficient circuit designs minimize ?
circuit pathways and length
What is the relationship between diameter and resistance
inversely
as cross sectional diameter of solid conductor increases, what happens to resistance
decreases
what do thicker wires offer
less resistance
how is the wire when the gauge number is lower
lower number, thicker wire
what is the relationship between temperature and resistance
directly related
what prevents electrons from flowing freely
increased atomic motion due to increased temperature
what happens to resistance when there is an increase temp
decreased resistance
(dont want it to heat up - Electronics engineers go to great lengths to minimize circuit heat build-up)
Ohms Law
V=IR
V= potential difference (volts)
I=Current (amperes)
R= resistance (ohms)
Power
P=IV
P=power (watts)
I=current (amperes)
V=potential difference (volts)
A generator converts what energy ?
Mechanical to electrical
Current flow is divided between branches of circuit
Parallel Circuits
What happens to total resistance, amperage and total voltage as more resistance is added to parallel circuit
As more resistances are added to a parallel circuit, total resistance drops, total amperage increases, and total voltage remains unchanged.
Rheostat
Variable resistor
Devices to circuits for protection
-circuit breaker
-fuse
what happens to circuit temps when resistance is added in a parallel circuit
Increases circuit temps
in what circuit do you add all the numbers together
series
in what circuit do you take the lowest number and cut it in half
Parallel
