Topic 2- Electricity Flashcards
same charges __ and opposite charges __
repel, attract
how do charged objects attract neutral?
the charges inside the neutral object move relatively when near charged object
can a neutral object attract a charged object?
yes
when objects are rubbed together what happens to the charge?
the charge is exchanged
charge in conductors:
move around
charge in insulators:
builds up, no flow
what does the ground do stop build-up of q?
accepts e’s
an electroscope measures the
magnitude of q of an object
if charges are free to move they will exert…
forces on each other and move until Fn on each q=0
in electrostatic equilibrium excess q in a ___ is located __
conductor
at the surface of it
coulomb law
Fe= k((q1q2)/r^2)
coulomb law relationship between forces on 2 charges
F1on2=-F2on1
electric field formula is k(Q/r^2)r what is the formula for the x component?
k(Qx/r^3)
the electric field is a ___ and is true for
property of space altered by the presence of charge
positive charges in the field
electrostatic force formula
F=qE
for + EF lines point
away
for - EF lines point
towards
an electric dipole is a vector pointing from
negative q to positive q in a dipole
electric dipole formula
p=qdi
the force on a dipole is proportional to the
gradient of the electric field
charge density 3D
charge per volume (C/m^3)
charge density 2D
charge per area (C/m^2)
charge density 1D
charge per length (C/m)
dot product formula
multiple x components then add multiple y components then add the multiply of z components
if vectors are perpendicular their dot product will be
0
work done is a l
line integral
work done formula
integral of: Fx ds(increment of the path)
what is a Gaussian surface?
a closed surface in 3D enclosing a volume
Gauss’s Law for electricity
EA(flux)= qin(total q inside a Gaussian surface)/Eo
Magnetic flux
E (dot product) dA
magnetic flux if at angle
EAcos(angle)
magnetic flux for spherical
E x 4pir^2
magnetic flux: outside sphere
1/4pie0 x Q/r^2
magnetic flux: inside a hollow sphere
0
magnetic flux: inside solid sphere
1/4pie0 x q/R^3 x r if (r>R)
EF inside a conductor
0
electrostatic work formula
W=F x ds
the electrostatic force is/isn’t conservative
is
when we say the electrostatic force is conservative what do we mean by conservative?
Wd by a force in a moving object from s1-s2 is independent of the path taken between 2 points
electrostatic potential energy graph the lines going upwards are from what charges?
2 negative
electrostatic potential energy graph the lines going downwards are from what charges?
negative and positive
as charges move closer together the electrostatic potential energy decreases/increases
decreases
electrostatic potential is also known as
voltage
electrostatic potential (V) formula
Ue/q (J/C=V)
change in an electrostatic potential relationship with electric field strength
V= -integral E (dot product) ds
what does the interaction of charged particles with a source charge?
an electric potential energy of a system of charges
what is the electric potential energy of a system of charges and units?
J it is work and is the work required to bring charges together
what is the electric potential of a system of charges and units?
V and it is the work per charge required to bring unit charge to a point in the electric field
is EPE or EP usually greater?
EPE
equipotential surfaces are
infinite parallel sheets
electric field lines are ___ to EPS
perpendicular
electric field lines point from low to high or high to low electric potential (V)
high to low (downhill)
if it is a negative charge (and on EPS) it will be at a region of what potential?
low
capacitors are
2 conducting plates separated by a vacuum
net charge of capacitors is
0
capacitance unit
Farrad
capacitance 2 formulas
Q/V or e0A/d
charge on a capacitator
Q=CE
capacitors in parallel
C=C1+C2….
capacitors in series
1/C= 1/C1+ 1/C2…
batteries are a collection of
cells tat maintain potential difference through chemical reactions
dielectrics are
an insulator that can support an induced Efield
current flows from
+ to -
current is scalar?
yes
in current electrons move which way and why?
opposite direction to I due to the electric field in conducting wire
current density vector points in what direction to EF
same
resistance is a measure of an objects ability to
resist an electric I
resistance in series vs parallel
series:
R=R1+R2…
parallel:
1/R=1/R1+1/R2
is resistance greater in a short thick wire or long thin
long thin
does ohms law hold for all conductors?
no
the gradient of a graph of I by V is
the conductance
series circuit VIRC:
voltage= V1+V2
current= I1=I2
resistance= R1+R2+R3
capacitance= 1/C=1/C1+1/C2
parallel circuit VIRC:
voltage= V1=V2
current= I=I1+I2
resistance= 1/R=1/R1+1/R2+1/R3
capacitance=C=C1+C2+C3..
Kirchhoff’s loop law states the
delta-V in a circuit is 0 ( for a conservative Ef) and non-conservative is delta mag flux
