Ch. 5: Electrostatics and Magnetism Flashcards
opposite charges exert what kinds of forces
attractive
like charges exert what kinds of forces
repulsive
what is a ground
a means of returning charge to the earth
what is the unit of charge
Coulomb
e = 1.6 E -19 C
what is the charge of a proton
+e
what is the charge of an electron
-e
how well does an insulator hold and transfer charge
do not easily distribute charge and will not transfer charge to another neutral object well
nonmetals
how well does a conductor hold and transfer charge
evenly distributes charge and will transport charges
metals and electrolytes
equation for Coulomb’s law
F = Kq1q2 / r^2
Force between two charges = [Coulomb’s constant * charge 1 * charge 2] / distance between charges, squared
Coulomb’s constant with units
k = 8.9E9 N * m^2 /C^2
which is stronger, gravitational or electrostatic force?
electrostatic force by ~10^40
what is Q
Q is the source charge that establishes a surrounding electric field
what is q
q is a test charge that enters an electric field
equation for E
E = F/q = kQ/r^2
what are the units of E
N/C
what direction do electric field vectors radiate given a positive source charge
electric field vectors radiate outward from a positive source charge
what direction do electric field vectors radiate given a negative source charge
electric field vectors radiate inward to a negative source charge
field lines
imaginary lines that represent electric field vectors for a source charge
how are density of field lines and field strength related
direct relation; stronger field = denser field lines
where is an electric field strongest
closest to the source charge
how is directionality of electric force related to directionality of electric field
electric field and electric force point in the SAME direction for POSITIVE charges
electric field and electric force point in OPPOSITE direction for NEGATIVE charges
equation for electric potential energy
U = kQq / r
EPE = coulomb’s constant * field * point charge / distance
when is electric potential energy positive
with like charges
when is electric potential energy negative
with opposite charges
definition of electric potential energy
work necessary to move a test charge from infinity to a point in space in an electric field surrounding the test cahrge
what causes electric potential energy to change
INCREASE - like charges towards each other, opposite charges away from each other (decrease stability)
DECREASE - like charges away from each other, opposite charge toward each other (increase in stability)
units of electric potential energy
J (EPE represents work)
definition of electric potential
ratio of the magnitude of a charge’s electric potential energy to the magnitude of the charge itself
equation for electric potential
V = U/q = kQ/r
what are the units of electric potential
V (volts) = J/C
when is electric potential positive
for positive source charges
when is electric potential negative
for negative source charges
voltage
potential difference between two points within an electric field
potential difference
delta V = Vb-Va = Wab/q
equipotential line
a line on which the potential at every point is the same (the potential difference between any two points is zero)
electric potential at a point charge near a dipole
V = [kq/r1] - [kq/r2]
perpendicular bisector of the dipole
plane that lies halfway between the dipole where electric potential is zero
electric potential at a point charge far from a dipole
V = [kqd/r^2] cos (theta)
net torque on a dipole
torque = pEsin theta
where theta is the angle the dipole makes with the electric field
magnitude of the dipole moment
p = qd
units of the magnitude of the dipole moment
Cm (coulomb meters)
magnitude of the uniform electric field produced by a dipole
E = [1/4pisigma naught] / [p/r^3]
in what direction with torque cause the dipole to orient
torque will cause the dipole to orient its dipole moment to the electric field
what creates a magnetic field
moving charges
what is the unit for magnetic field strength
tesla (T) or [N * s] / [m * C]
diamagnetic materials
COMMON materials (wood, skin, glass)
paramagnetic materials
weakly magnetized in the presence of an external magnetic field
aluminum, copper, gold
ferromagnetic materials
strongly magnetized when exposed to a magnetic field or under certain temperatures
iron, nickel, cobalt
how do field lines flow in a bar magnet
from north pole to south pole
equation for magnetic field produced by a long and straight current carrying wire
B = [mu naught * I] / [2pir]
where r is a perpendicular distance from the wire
permeability of free space
mu naught = 4pi E -7 T*m/A
equation for magnetic field at the center of a circular loop of current carrying wire
B = [mu naught * I] / [2*r]
where r is the radius of the loop
what do magnetic fields exert their forces on
moving charges only
Lorentz force
sum of electrostatic and magnetic forces
equation for magnetic force exerted on a charge in a magnetic field
F = qvB sin theta
equation for magnetic force of a current carrying wire
F = ILB sin theta
