Midterm #1 Flashcards
inductors and capacitors always cause _________
phase shifts
whenever a charge is created, an ____ charge of the ______ sign is created at that same time
equal, opposite
grounding
conducting object is grounded if its connected to the earth or other electron well via conductor, allowing the transfer of charge from earth’s large reservoir
objects can be charged by _____ with each other to obtain the ____ charge
contact, same
How can you permanently charge an object?
ground an object then cut the wire, the electrons have to stay in the object. Becomes charged.
charging by induction example
two metal balls touching. Positively charged object brought near them, electrons flow from one ball to the other to balance the positive charge. Balls are separated before the positive charge is removed, electrons stay in the ball that was closest to the positive charge.
coulombs law equation
write
electric field equation
E=F/q
magnitude of electric field E created by point charge Q
E=KQ/r^2
field lines begin on ____ and end on ____
positive, negative
more field lines indicate
stronger charge
how do field lines add?
like vectors
draw the field lines for opposite charges next to each other
draw
draw the field lines for like charges next to each other
draw
Charge will collect at _____ in a conductor
all points
conductors allow ___ to move within it. Electrical forces will cause ______ to move inside it until equilibrium is reached. ______ move until the field is perpendicular to the surface
free charge
insulators have _____ inside of them, conductors don’t
field lines
draw electric field between two uniform plates
draw
draw electric field between two uniform plates
draw
Electrical potential
potential energy per unit charge
units for volts
J/C
mechanical energy
kinetic energy + potential energy
a charge accelerated by an electric field causes ______ energy to convert to _______
electric potential, kinetic
current flows ____ to _____
Electrons flow ____ to ____
positive to negative
negative to positive
Electric potential at any point in space near an arrangement of multiple charges is equal to ____
the sum of the potentials created by each individual charge
equipotential lines? How are they drawn?
lines that show where the electric potential is constant. Are always perpendicular to electric field lines.
How much work is needed to move a charge from one spot on an equipotential line to another on the same line?
None! Lines are all at the same level
Amount of charge a capacitor can store depends on
the voltage and the physical characteristics of the capacitor
How do dielectrics work?
By polarizing. They cancel out some of the charge stored on the plates allowing more to be put there before it equals out the dielectric.
dielectrics must be excellent isulators
capacitors in series
total capacitance is less than any one of the individual capacitors
current units
I=C/s
the voltage drop across a resistor in a simple circuit is _____ to the voltage of the battery
equal
How do resistance and resistivity change with temperature?
higher temperature is generally more resistant because the electrons are vibrating making less room for charge to pass through
What shapes make the best resistors?
thinner and longer
two parts of every voltage source
a source of electrical energy and an internal resistance
EMF
potential difference of a source when no current is flowing
true potential difference on chemical level, but not accessible due to internal resistance.
formula for terminal voltage
V=emf-internal resistance
when multiple voltage sources are in series, their internal resistances and EMF’s _______
add algebraically
terminal voltage= emf when
no current is flowing
Two voltage sources with identical emf in parallel have ______ total resistance than the individual sources and thus deliver more current to the source
smaller
Kirchoffs rules
sum of all currents entering a node equals the sum of all currents leaving it
sum of changes in potential energy along any loop= zero
batteries in parallel increase
capacity
batteries in series increase
voltage
RC circuit
resistor and capacitor (Tao=RC)
Time constant Tao
how long it takes to charge a capacitor in an RC circuit
magnetic poles always come in ____
pairs
North pole of magnet is attracted to the _____ pole of geographical earth
north
all magnetism is created by ________
electric current
ferromagnets
those that exhibit strong magnetic effects, atoms in ferromagnets act as small magnets and align in domains with each other. Domains can grow creating permanent magnets
In a magnet, all electrons have ______
the same spin
how to make a permanent magnet
heat up a material, expose it to a magnet while its hot, then let it cool next to the magnet
field lines run _______ and go ____ the magnet
north to south, through
electromagnet
motion of charges from current produces magnetism
magnetic field lines
field is tangent to the magnetic field line
strength shown with more lines
cant cross
are continuous loops
units for magnetic force
Tesla= N/Axm
right hand rule
thumb= v
pointer=b
middle=f
magnetic force only acts on ____ electric charges
moving. They can effect stationary magnets because each magnet has moving charges inside of it! (Lorentz force)
If the magnetic field and velocity are parallel
no force
when can the magnetic force supply centripital force and cause a charged particle to move in a circular path?
when velocity and magnetic force are perpendicular
Hall effect
creation of voltage across current carrying conductor by magnetic field (net deflection of moving charges creates imbalance across the conductor= voltage difference from one side to the other inside the conductor)
magnetic field can exert ____ on a current carrying wire
torque
magnetic field solenoid
strong inside, almost none outside
magnetic flux
Magnetic flux is a measurement of the total magnetic field which passes through a given area
any change in flux ______
induces an emf and is defined as electromagnetic induction
increased angle= ____ flux
less
magnetic induction
movement of a magnet or coil through the other produces an emf. The greater the speed, the greater the emf.
how do generators work?
rotating a coil inside a magnetic field
Lentz law
current will oppose the change in magnetic flux
motors convert _____ energy to ______ energy.
electrical to mechanical
generators convert _____ to ______
mechanical energy to electrical energy
any rotating coil will ____
have an induced emf
back emf
in motors when the coil rotates, it creates an emf that opposes the emf input to the motor
transformers
use induction to transform voltages from one value to another. Have primary/secondary currents and voltages
step up transformer
higher voltage, less current
stem down transformer
lower voltage, higher current
For which type of current to transformers work?
AC. NEVER DC.
inductance
property of device that tells how effectively it induces an emf in another device.
mutual inductance
effect of two devices inducing emf’s in each other. CHange in current in one induces an emf in the other
self inductance
effect of device inducing an emf on itself
inductance is determined by
purely the geometry of the conductor
the larger L is, the more ______ the inductor ______ changes to the current
strongly, opposes
inductors make it impossible to turn current _____ instantaneously
off
RL circuit
battery/reisistor/inductor in series
resistors in series
same current
resistors in parallel
same voltage
glass rod with silk charges
glass positive
silk negative
electrostatic force is stronger than
gravity
why do charges accumulate at points?
although they repel each other, the charge is technically evenly distributed throughout the material
electric potential is _____, electric field is _____
scalar, vector
dielectric strength
max electric field strength above which an insulating material begins to break down and conduct
superconductors
have zero resistance
Energy equation
Energy=Power x Time
how to find v and I for AC
peak voltage/current divided by square root of two
why AC?
allows for use of transformers, which can be used to change voltages (higher efficiency)
what is a short in a wire?
undesired low resistance path in a circuit
why do lights dim when a large appliance is turned on?
the large current the appliance motor draws causes significant IR drop in the wires and reduces the voltage across the light
terminal voltage
V= emf-IR where I is current and r is resistance (including the load resistance)
parallel voltage sources produce more
current
ferromagnets
those materials that exhibit strong magnetic effects
curie temperature
above this temperature, magnetism is lost
difference in generated magnetism between ferromagnets and electromagnets
ferromagnets- electrons posses angular momentum that produces the magnetism
electromagnets- have a motion of charge b y current that produces the magnetism
magnetic field of a circular loop
looks just like the magnetic field of a bar magnet
magnetic field of a long straight wire
forms circles perpendicular to the wire
when does a charged particle move in a circular motion?
when its moving perpendicular to the uniform magnetic field
parallel currents ______ while opposite currents _____
attract, repel
