Class Four Flashcards
value of elementary charge
e = 1.6 x 10-19 C
what does it mean when charge is quantized
charge on an object can only be a whole number of e’s
charge is quantized formula
q = n (+/- e)
Coulomb’s law
Coulomb’s constant
9 x 109 N.m2/C2
principle of superposition
adding the resulting forces
source charges
the charges that create an electric field
electric field formula
E = k(Q/r2)
electric force & field formula
F = qE
conductors
contains charges that are free to roam throughout material
most important conductors
metals
insulators
don’t have free charges → electrons are tightly bound to their atoms
if an object moves with nature..
its potential energy decreases
if an object moves against nature..
its potential energy increases
electric potential formula
= k (Q/r)
positive charges want to move to regions of..
lower potential
negative charges want to move to regions of..
higher potential
what causes a net movement of charge
electrons’ drift velocity
current formula
I = Q / time
what is current
charge over time
what creates a current
voltage
resistance formula
R = V / I
voltage / resulting current
resistance and resistivity formula
R = p (L/A)
p = intrinsic resistivity
L = length
A = area
Ohm’s law
V = IR
voltage = current x resistance
what is a resistor
component in an electric circuit that has a specific + known resistance
when are resistors in series
if they follow eachother along a single connection in a circuit
when are resistors in parallel
when they provide alternative routes from one point in a circuit to another
how do we combine resistors in series
we add them together
how do we combine resistors in parallel
take the product of the resistors
and then divide it by the sum
R1R2 / R1 + R2
job of a voltage source
maintain a potential difference between terminals
positive terminal
longer line → higher potential
negative terminal
shorter line → lower potential
resistors in series always share the same..
current
resistors in parallel always share the same..
voltage
Kirchhoff’s law
at a junction in an electrical circuit, the sum of currents flowing into the junction is equal to the sum of currents flowing out of the junction
power dissipated by a resistor: joule heating law
P = I2R
what do voltmeters do
measure the potential differences between 2 points in a circuit
what do ammeters do
measure the current through a particular point in the circuit
what is a capacitor
a pair of conductors that can hold equal but opposite charges
charge on a capacitor formula
Q = CV
charge on capacitor = proportionality constant x potential diff between the plates
what is capacitance dependent on
sizes of the plates and how far apart they are
capacitance formula
C = e (A/d)
e = permittivity of free space (constant)
A = area
d = diameter
2 purposes of a parallel plate capacitor
create a uniform electric field
store electrical potential energy
Ed’s formula
V = Ed
used with parallel plate capacitor
feature of a parallel plate capacitor
electric field is the same magnitude at every point between the plates
electrical PE stored in a capacitor formula
PE = ½QV
what are dielectrics
insulating material that goes in-between capacitance plates
purpose of dielectrics (2)
keeps plates from touching
increases capacitance
what happens when you disconnect the battery and insert dielectric (4)
C increases by a factor of K
Q stays the same
V decreases by a factor of K
E decreases by a factor of K
what happens when you keep the battery connected and insert dielectric (4)
C increases by a factor of K
Q increases by a factor of K
V and E stays the same
if charge is held constant and capacitance increases,
PE decreases
sif voltage is held constant and capacitance increases..
PE increases
