concept 4c Flashcards
fundamental unit of charge
1.60e-19 C
a proton and an electron have the same amount of charge
proton is positively charged (+1.60e-19)
electron is negatively charged (-1.60e-19)
insulator
material that resits the movement of charge bc the electrons are tightly associated with their nuclei
not easily distribute a charge over its surface
will not transfer that charge to another neutral object very well
conductor
material that allows the free movement of electrical charge
one with very low or zero resistance
charges distributed evenly upon surface of the conductor
able to transfer and transport charges
often used in circuit or electrochemical cells
Coulomb’s law
relates the electrostatic force between 2 charged particles to their charges and the distance b/w them
quantifies he magnitude of electrostatic force (Fe)
Fe=kq1q2/r^2
Coulomb’s constant
aka electrostatic constant
k
number that depends on the units used in the equation
8.99e9 Nm^2/C^2
permittivity of free space
E(sub0)
8.85e-12 C^2/Nm^2
Electric Field
electric charge have surround electric field
exerts force on other charges that move into the space of the field
this force can be attractive or repulsive depending on the source charge and the test charge
E=Fe/q=kQ/r^2
source charge (Q)
produces and an electric field
if same as test charge the force is repulsive, if opposite of test charge the force is attractive
test charge (q)
charge that is placed in the electric field
when in electric field it will experience an electrostatic force (Fe) that is equal to qE (chargeXmag. of electric field)
field lines
imaginary lines that represent how a positive test charge would move in the presence of the source charge they point away from positive charges point toward (in) negative charges point from all surfaces of charge (form shape similar to bike wheel)
types of potential energy
gravitational
elastic
chemical
electrical
electrical potential energy (U)
depends on relative position of one charge w/ respect to another charge or collection of charges
U=kQq/r
if like charges U will be positive
if unlike charges U will be negative
is the work necessary to move a test charge from infinity to a point in space in an electric field surround a source charge
changing electrical potential energy
will increase when 2 like charges move toward each other or when 2 opposite charges move apart
will decrease when 2 like charges move apart or when 2 opposite charges move toward each other
electrical potential (V)
measure of electrical potential energy per unit charge
given in volts (V)
V=U/q=kQ/r
potential difference
difference of electrical potential b/w 2 distinct points
measured in volts
aka voltage
differences in electrical potential also drive current as electromotive force in a circuit
=Vb-Va=Wab/q (Wab is work needed to move test charge thought electric field from point a to b )
equipotential line
line on which the potential at every point is the same, thus the potential difference is 0
in 3D space they look like spheres surround the source charge
electric dipole
separation of equal and opposite charge by a small distance
can be seen in polar molecules
dipole moment (p)
p=qd
q is the charge and d is the separation distance
potential bisector of the dipole
equipotential in that lies halfway b/w +q and -q
has electric potential of 0 at any point along this plane
mag of he electric field is E=1/4piE(sub0)Xp/r^3
magnetic field
any moving charge create a magnetic field can be a single electron traveling though space or a current through a conductive material unit tesla (T) for small magnetic fields measured in gauss 1T=10^4 gauss
classifying material
diamagnetic
paramagnetic
ferromagnetic
diamagnetic material
made of atoms with no unpaired electrons
have no net magnetic field
materials slightly repelled by a magnet so are weakly antimagnetic
common material you wouldn’t expect to stick to magnets: wood, plastic, water, glass, skin, etc.
paramagnetic materials
atoms with unpaired electrons
have net magnetic dipole but no net magnetic field
weakly magnetized in presence of external magnetic field
aligning magnetic dipoles with the external field
aluminum, copper, gold
ferromagnetic materials
have unpaired electrons
permanent atomic magnetic dipoles, oriented randomly so no net magnetic dipole
become strongly magnetized when exposed to magnetic field or under certain temps
iron, nickel, cobalt
bar magnets
magnetic field for long straight wire
B=u0I/2(pi)r
u0=mu not. permeability of free space= 4piX10^-7 Tm/A
magnetic field for circular loop
B=u0I/2r
pi is not included
right-hand rule for magnetic field
point thumb in direction of the current
wrap fingers around the current-carrying wire
fingers mimic the circular field lines, curling around the wire
Lorentz force
the sum of the electrostatic and magnetic forces acting on charges
magnetic force
force exerted on a charge that moves in a magnetic field
Fb=qvBsin(theta)
q is charge, v is velocity, B mag of magnetic field, theta is b/w v and B (sin 0 and 180 equals zero)
right-hand rule for magnetic force
to determine direction fo magnetic force:
position right thumb in direction of velocity
put fingers in direction of magnetic field lines
curl fingers toward direction of force
Fb on a current-carrying wire
Fb=ILBsin(theta)
same right hand rule for magnetic field
current
the flow of positive charge but negative charges are actually moving I=Q/delta t unit ampere (1 A=1C/s) direction of current is opposite direction of electron flow
conductivity
2 types: metallic and electrolytic
metallic conductivity
conductivity in solid metals and the molten form of some salts
can easily lose one or more of their out electrons, then free to move around in larger collection of metal atoms
most metals are good electrical and thermal conductors
electrolytic conductivity
conductivity in solutions
depends on the strength of a solution
sea water and orange juice are better conductors than di water
metallic bond
sea of electrons flowing over and past a rigid lattice of metal cations
more accurately described as an equal distribution of charge density of free electrons across all of neural atoms within metallic mass
direct current (DC)
charge flows in one direction only
current in household batteries
alternating current (AC)
flow changes direction periodically
current supplied over long distances to homes and buildings
galvanic (voltaic) cell
can produce a potential difference
spontaneous oxidation-reduction rxns that generate emf as a result of potential difference
standard batteries
electromotive force (emf)
voltage when no charge is moving b/w the 2 terminals of a cell that are at different potential values
not actually a force but a potential difference
“pressure to move” that results in current
Kirchhoff’s laws
2 rules that deal with the conservation of charge and energy within a circuit
junction rule and loop rule
junction rule
current into junction=current leaving junction
loop rule
Vsource=Vdrop
draw loop and add/subtract parts and set equal to zero
resistance
opposition within any material to the moment and flow of charge
materials w/ no resistance are conductors
materials w/ high resistance are insulators
resistors
conductive materials that offer amounts of resistance between conductors (no resistance) and insulators (high resistance)
properties of resistors
resistance is dependents on characteristics of the resistor: resistivity, length, cross-sectional area, and temp.
R=pL/A
p is resistivity, L is length, A is area
resistivity
measure of intrinsic resistance of a material independent of its shape or size
generally increases with temp
depends on the material of the resistor
length
longer resistor greater resistance (bc electron has to travel a greater distance thought resistant material)
cross-sectional area
inversely proportional to resistance
if area is doubled, resistance is halved
the wider the resistor the more current can flow, decreasing resistance
conduction pathways
number of pathways through the resistor
increasing the area increases the conduction pathways
temperature
most conductors have greater resistance at higher temperatures
due to increase thermal oscillation of atoms, producing greater resistance to electron flow
Ohm’s Law
relates voltage, current, and resistance for a given circuit element
V=IR–> I=V/R and R=V/I
basic law of electricity
power
rate at which energy is transferred or transformed
P=W/t=delta E/t
power of resistor
rate at which energy is dissipated by a resistor
P=IV=I^2R=V^2/R
resistors in series
current flows thought each resistor there is a voltage drop w/ each resistor voltage drop--> 1/V=1/V1+1/V2+... resistance--> R=R1+R2+... R increases as resistors are added
resistors in parallel
allow charge to follow different parallel paths b/w high-potential terminal and low-potential terminal
V=V1+V2+…
1/R=1/R1+1/R2+…
capacitors
characterized by their ability to hold charge at a particular voltage
2 electrically neutral metal pates connected to a voltage source
capacitance
ratio of magnitude of the charge stored on one place to the potential difference (voltage) across the capacitor C=Q/V unit farad (1F=1C/V)
capacitance of parallel plate capacitor
dependent upon the geometry of the 2 conduction surfaces
C=E0(A/d)
E0=8.85e-12
there is a uniform electric field b/w the 2 plates E=V/d
potential energy stored in a capacity
U=1/2CV^2
dielectric material
insulation (insulating material)
used to increase capacitance
air, glass, plastic, ceramic, certain metal oxides
dielectric constant (kappa)
how much the material increase the capacitance by
measure of materials insulating ability
capacitance due to dielectric material
C(sub d)=(kappa)C
dielectric constant X capacitance w/o material
capacitors in series
total capacitance decreases, and decreases as more capacitors are added
1/C=1/C1+1/C2+…
capacitors in parallel
total capacitance equal to the same of individual capacitance
C=C1+C2+…
meters
the devices that are used to measure circuit quantities in the read world
ammeters
used to measure the current at some point within a circuit
inserted in series
high current will overwhelm the ammeter, low resistance shunt is used in parallel to allow reading
voltmeter
requires a circuit to be active
use magnetic properties of current-carrying wires
used to measure the voltage drop across 2 points in a circuit
wired in parallel
ohmmeter
does not require a circuit to be active
often have their own batter of known voltage and function as ammeters
