Electrostatics and Magnetism Flashcards
What causes a system to become electrically unstable?
Unbalance of charges
What is grounding?
The transfer of excess electrons from an object to back to the Earth
What is the SI unit for charge?
Coulomb
What are the charges of a proton and a electron?
+/- 1.60E-19 C
Insulators?
Do not easily distribute charge over its surface
Do not transfer charge to other neutral objects
Usually their electrons are closely linked with the nuclei
Most nonmetals
Conductors?
Easily distribute charge about evenly upon the surface
Able to easily transfer charges
Often used in circuits and electrochemical cells
Nuclei are surrounded by a “sea” of free e-s that are able to quickly move throughout the material
Usually metals and ionic (electrolyte) solutions
What is Coulomb’s Law and what does it represent?
F(electric) = kq(1)q(2)/r^2
It quantifies the magnitude of electrostatic force between two charges
Difference between test charge (q) and source charge (Q)
test charge (q) is the charge placed in the electric field
source charge (Q) is the charge that creates the electric field
Properties of an electric field
Every electric charge sets up an electric field
They exert force on other charges that move into their space of field
Whether the force is attractive or repulsive depends on both the test charge and the source charge
What are the two methods (equations) of calculating electric field?
E=Fe/q
[Electric Field=magnitude of force felt by source charge/test charge]
E=kQ/r^2
[Electric Field=constant x magnitude of source charge/distance between charges or points of interest]
How is the direction of electric field vectors determined?
The potential movement if a positive test charge were placed within the field
+ charges point outward, - charges point inward
What is the equation for electrical potential energy? What other factor is it equal to?
U=kQq/r
Potential Energy = Work
In relation to electrical potential energy, when are two molecules most stable?
When the PE is small
*Potential energy inversely proportional to stability
(Opposite charges, very negative large number; like charges, very small number due to large distance)
What is the magnitude of the charge of an electron?
1.6x10^-19C
What are the three equations for the electric potential?
V=kQ/r
V=U/q
V=Vb-Va=Wab/q
Towards what energy will charges spontaneously move?
Whatever direction decreases their potential energy
How will electric potential be affected by charges spontaneously moving? (negative and positive)
Positive charges will spontaneously move in the direction that decreases their electrical potential (negative voltage)
Negative charges will spontaneously move in the direction that increases their electrical potential (positive voltage)
~But in both cases the electrical potential energy is decreasing
What are equipotential lines?
A line on which every point has the same potential
Is work dependent on the pathway between two points?
No, work depends on the potential difference but not the pathway taken between them
What is the equation for the electric potential near a dipole?
V=kqdcosΘ/r^2
d=distance between two charges
r=distance between point in space to the midpoint of the dipole
What is the equation for a dipole moment (p) and what is the SI unit?
p=qd in Cm (Coulomb x meters
where q is the product of charge
What is the perpendicular bisector of the dipole? and what is the electric potential here?
the plane that lies halfway between +q and -q
the angle between this plane and the dipole is 90 degrees (cos90=0) so the electric potential along this plane is 0
What is the equation for torque on a dipole?
T=pEsinΘ
p=dipole moment
E=electric field
Θ= angle the dipole makes w the electric field
What effect will torque have on dipole?
Torque will cause the dipole to reorient itself so that its dipole moment aligns with the electric field
(sin0 = 0 ~ torque = 0)
What creates a magnetic field?
any moving charge
What is the SI unit for magnetic field strength?
Telsa (T)
1 T = 1 N s / m C
What are the three types of magnetism?
Diamagnetic, paramagnetic, ferromagnetic
Diamagnetic materials
made of atoms with no unpaired electrons and no net magnetic field
slightly repelled by magnets, weakly antimagnetic
includes wood, plastic, glass, water, skin
Paramagnetic materials
weakly magnetized in the presence of external magnetic fields
contains unpaired electrons, but atoms are randomly oriented so there is no net magnetic field
includes aluminum, copper, and gold
Ferromagnetic materials
strongly magnetized when exposed to magnetic fields or certain temperatures
unpaired electrons and permanent magnetic dipoles, but not net magnetic dipole
includes iron, nickel, and cobalt
What orientation are field lines?
Exit the north pole, enter the south pole
Can a magnet be monopolar?
Field lines are circular so it would be impossible
What determines the configuration of the magnetic field lines surrounding a current carrying wire?
Depends on the shape of the wire
What is the equation for the magnitude of the magnetic field produced by the current in a STRAIGHT wire?
B=μ I/2πr
B=magnetic field
μ=permeability of free space (4π x 10^-7 Tm/A)
I=current
r=distance from the wire
What “rule” do the field line circles of a wire follow?
The “right handed rule” in which if you point your thumb in the direction of the current, the directions your fingers wrap around is the direction the concentric field lines curl around the wire
What is the equation for the magnitude of the magnetic field produced by the current in a CIRCULAR LOOP wire?
B=μ I/2r
B=magnetic field
μ=permeability of free space (4π x 10^-7 Tm/A)
I=current
r=distance from the wire
What do magnetic fields exert forces on?
only on other moving charges
What is the Lorentz force?
The sum of the electrostatic and magnetic forces acting on a charge (since charges often have both acting simultaneously)
What is the equation for magnetic force acting on a moving charge in a magnetic field?
F=qvBsinΘ
q=charge
v=magnitude of velocity
B=magnitude of magnetic field
Θ=smallest angle between vector v and magnetic field vector B
*sine means the charge must have a perpendicular component of velocity in order to experience a magnetic force - if its moving parallel, it wont experience a force
What “rule” is used to determine the direction of the magnetic force on a moving charge and how is it used?
The “right handed rule” is used by positioning your right thumb in the direction of the velocity vector then putting your fingers in the direction of the magnetic field lines
Your palm will point in the direction of the force vector for positive charges and the back of your hand will point in the direction of the force vector for negative charges
In terms of magnetic force, what is the relation between direction of velocity and force?
The velocity and force will always be perpendicular to each other
What is the equation for the magnitude of magnetic force felt for a straight wire?
F=ILBsinΘ
I=current
L=length of wire in the field
B=magnitude of magnetic field
Θ=angle between L and B
*Can also use the right handed rule
Current is the flow of what?
Positive charge
What requirements is a magnetic force?
must have an electric field acting on a charge moving any direction but parallel/antiparallel
