Electricity Flashcards
Measuring force of attraction of repulsion between charged objects
F = kq1q2/r^2
coulombs
Universal Law of Conservation of Charge
Universe has no net charge
What is the smallest possible unit of charge?
one electron unit which is 1.6 X 10^-19 C, the charge on one electron or one proton
Center of charge
Where the charge is considered to have thought to be originated even though there may be no charge at it.
What is a Field
Distortion in space that creates a force on a charge. This force created by fields can act at a distance
What is an electric field
Electrostatic force per unit charge (N/C, V/m)
What is force of an electric field?
F = Eq
Potential energy of a charge in an electric field
U = qEd
on earth
Voltage
Potential for work by an electric field in moving any charge from one point to another given in units of volts (V = J/C). Voltage is scalar so voltages can be summed up directly.
Voltage = PE/q = E*d
Voltage due to a point charge
V = k q1/r
Is Work done by an electrostatic field path dependent? Why or why not?
Path independent
Electric field is conservative; conserves mechanical energy
Equipotential surfaces
points perpendicular to an electric field. All points on an equipotential surface are at the same voltage.
Electric dipole moment
p = qd
Current
Moving charge given in amps (A = C/s)
scalar, flow to be in the direction of the movement of positive charge
i = V/R, or VIR
Circuit
a cyclical pathway for moving charge where a battery provides the potential difference (voltage) needed to maintain charge flow
Resistivity
Resistance to the flow of charge
Resistance (R)
quantitative measure of an object of a particular shape and size to resist the flow of charge. Measured in ohms.
wires that are long and have a great cross sectional area have the greatest resistance
Flow rate of a real fluid moving through a horizontal pipe with constant diameter
Q = change in pressure / resistance
Battery
adds energy to a circuit; battery pumps the fluid to a greater height and rated by EMF, another word for voltage
Capacitor
temporarily store energy in a circuit; stores it in a form of separated charge
Parallel plate capacitor
two plates separated by a very small distance. One plate holds positive charge, and the other plate holds the exact same amount of negative charge. This separation of charge creates an electric field that is constant everywhere between the plates
Electric field in a parallel plate capacitor
q/dielectric times Q/A
greater the area, greater the charge, greater the electric field of the plate capacitor
Capacitance
the ability to store charge per unit voltage; something with a high capacity can store a lot of charge at low voltage
C = Q/V
Amount of charge that can be stored directly on each plate in relation to area, and distance
Greater the area, greater the amount of charge that can be stored on each plate
The farther the plates are separated, the greater the voltage, and lower the capacitance
Energy stored in any shape capacitor
U = 1/2 (QV) = 1/2 (CV^2) = 1/2 (Q^2/C)
in a fluid capacitor, what would a g*change in height be equal to?
voltage
dielectric in a capacitor
An insulator lodged between the plates to break the circuit and store energy in the circuit.
Case of no battery: Increase capacitance by decreasing the voltage - the negatives and positive lined up in the capacitor get canceled by the molecules that are polarized in the dielectric.
Battery inserted: increase capacitance by increasing the charge stored. When the battery is inserted, the battery tries to make the voltage the same across the circuit. So it inserts more charge to compensate for those charges that are canceled out.
dielectric of a non-conducting material
always greater than 1
The point of some maximum voltage the dielectric will break down and conduct electricity
the dielectric strength
Resistors in series
Total resistance is R1 + R2 + …
Resistors in parallel
1/R = 1/R1 + 1/R2 + …
Capacitors in series
1/C = 1/C1 + 1/C2 + …
Capacitors in parallel
C = C1 + C2 + ….
Electric potential, V
Voltage is a “difference in electric potential”
Scalar or vector?
Potential for work by an electric field in moving any charge from one point to another - random numbers in space
V = Ed = PE/q
Voltage due to a point charge:
kq1/r: q creating that voltage) = J/C or Change in unit is Volts
scalar quantity
Electromagnetic field
Light
change in E creates a change in B, change in B then creates a change in E, E and B are perpendicular to each other
propagating outward creating a wave of its own independent existence in direction of velocity, c = 3*10^
they can travel through a vacuum; don’t need a medium
Potential energy from electric field derived from a point charge
U = kq1q2/r
Dipole in an electric field
align itself opposite orientation to the field
Magnetic field
unit: tesla = QvB
produced only by moving charges so a moving charge creates or induces both magnetic and electric field
exerts a centripetal force on a moving particle
qBv = mv^2/r
non-conservative force
Does magnetic field create force on a static electric charge?
Nope
T/F A moving charge induces both a magnetic and electric field
T
Why doesn’t a moving charge through a magnetic field increase its speed?
Because no work can be done by the force (cos 90 = 0) and W = F*d cos(0). This force does no work so it cannot transfer energy to the particle to increase the speed of the particle.
Why does a charged particle moving through a magnetic field go through a circular path?
Magnetic force perpendicular to both the velocity and magnetic field causes the particle to go onto a circular path
gyroradius
The radius of the circular motion of a charged particle in the presence of a uniform magnetic field.
r=mv/qB .
Electric potential energy
PE = F*d = qEd
