Lect 7: Electricity and Magnetism Flashcards
intrinsic property of some subatomic particles
positive and negative 1.6 * 10^-19 C
quantied to discrete levels
SI Unit = Coulomb
charge (q)
universe has 0 net charge; Net charge is created by separating electrons from protons
If a negative charge is created, a positive charge must be created
law of conservation of charge
describes the magnitude of the force of attraction / repulsion between two charged objects (point charges)
Coulomb’s Law
Equation: Coulomb’s Law
F = k * q1 * q2 / r^2
Note: k = Coulomb’s constant = 8.9 * 10^9 N*m^2 / C^2
point where the charge of an object is considered to originate
center of charge
concept to explain action at a distance
create forces of gravity, electricity, and magnetism
field
represent any field
point in the direction of a field: Positive —> Negative
relative distance between lines shows strength of field
can never intersect
lines of force
electrostatic force per unit charge
vector in the direction of the field
SI Unit = N/C or V/ m
electric field (E)
Equation: Electric Field from a point charge
E = k * q / r^2
SI Unit: N / C
Equation: Electrostatic force on a point chargee
F = E * q
Equation: Potential Energy (U) of a point charge in an electric field
U = F * d = E * q * d
SI Unit: Joule
Note: d = displacement from arbitrary 0 point
the potential for work by an electric field in moving any charge by a distance (d)
SI Unit = Volts (V) and J/C
voltage
Equation: Voltage
V = E * d
Equation: Voltage due to a point charge
V = k * q / r SI = V or J/C
Work done by an electric field is _______ of the path because the field conserves mechanical energy
independent
movement perpendicular to the electric field doesn’t cause a change in potential; all points on this surface are at the same voltage
equipotential surface
created by two opposite charges w/ equal magnitudes; aligns itself in the opposite orientation to the field when placed in an electric field
electric dipole
allows electrons to flow relatively freely; holds excess charge on the surface of the material; if uniformly charged, the electric field = 0
Ex: Metal
conductor
holds electrons tightly in place; poor conductors
Ex: network solids (glass, diamond)
resistors
to charge a conductor w/ a charged object
Ex: negatively charged rod placed near a good conductor that is near a second conductor causes electrons to move from the first to the second conductor, leaving the first one w/ a positive charge
induction
a moving charge; scalar quantity
flow is in the direction of POSITIVE charge; created by the flow of electrons but is in the direction that a positive charge would flow
SI = Amp (A) or C/sec
current (I)
cyclical pathway for a moving charge
circuit
quantitative measure of how a substance resists the flow of charge
resistivity (rho)
quantitative measure of an object w/ a certain shape/size to resist flow of charge; if the length of wire / area is cut in half, the object’s ___ is doubled
proportional to LENGTH and inversely proportional to AREA
SI Unit = Ohm (Ω)
resistance (R)
product of R and I = voltage (V); equation used to analyze circuits
Ohm’s Law
Equation: Ohm’s Law
V = I*R
a current flowing into a node must = the current flowing out; (A node is any INTERSECTION of wires)
Kirchoff’s 1st rule
voltage around any path in a circuit must sum to 0
Kirchoff’s second rule
measurement used to rate batteries, which add energy to increase the voltage between two points
Note: Assume NO internal resistance on MCAT
Electromotive Force (EMF)
used to temporarily store energy in a circuit in a separated charge
capacitor
two conductive plates separated by a small distance; 2 plates hold = amounts of opposite charges; creates a constant electric field between the two plates
parallel plate capacitor
the ability to store charge / unit voltage; a substance with high _____ can store a lot of charge at low voltage
proportional to charge and inversely proportional to voltage
–charge is only on the inside face of each plate; thickness of the plates does not affect charge stored
capacitance
Each unit of charge added causes the _______ to increase proportionally
voltage
Equation: Charge w/ capacitance & voltage
graph produces straight line; area under the curve = Energy (Q * V)
Q = C * V
Equation: Capacitance
SI Unit: Farad (F)
C = Q / V
Equation: Energy (U) stored by a Capacitor w/ charge and voltage
U = 1/2 * Q * V
Equation: Energy (U) stored by a Capacitor w/ capacitance and voltage
U = 1/2 * C * V^2
Equation: Energy (U) stored by a capacitor w/ charge and capacitance
U = 1/2 * Q^2 / C
substance between the plates of a capacitor; must be an insulator
resists creation of an electric field so plates (capacitor) can store more charge
increases capacitance and amount of Energy (U) stored in the capacitor
dielectric
dielectric constant = k
components in a row (i.e. train cars)
any two components not separated by a node
components in series
single components in alternate paths connecting the same nodes
components in parallel
Equation: Resistors in Series
R(eq) = R1 + R2 + R3…….
Equation: Resistors in Parallel
R(eq) = 1/R1 + 1/R2 + 1/R3……
Equation: Capacitors in Series
C(eq) = 1/C1 + 1/C2 + 1/C3…
Equation: Capacitors in Parallel
C(eq) = C1 + C2 + C3…
Electric and mechanical are the SAME
used to integrate electricity and mechanics into the same question
Ex: Given V & I of a machine, how quickly can it life a mass (m) to height (h)?
Power
Set electric power = to mechanical power only when _____
energy is dissipated as heat by a resistor
Equation: Power w/ current and voltage
P = I * V
Equation: Power w/ current and resistance
P = I^2 * R
Equation: Power w/ voltage and resistance
P = V^2 / R
rate at which heat is generated as current goes through a resistor
power dissipated
net movement of electrons is unidirectional in a circuit
direct current (dc)
The movement of _______ creates power
electrons
current created by oscillating electrons back and forth in simple harmonic motion; voltage or current described by sine wave
alternating current (ac)
Max current occuren when electrons are at their max ______
voltage
Equation: Max Voltage
V(max) = √2 * V(rms)
Equation: V(rms)
V(rms) = V(max) / √2
Equation: I(rms)
I(rms) = I(max) / √2
field created by changing electric field; created by moving charge or current; has N and S pole; like poles repel
represented by force lines that point from the north pole to the south pole
magnetic field (B)
magnetic strength follows inverse square rule except in ______
long straight wire
Equation: Force on a charge moving through a magnetic field w/ velocity
F = q * v * B * sin(ø)
Note: ø = angle between magnetic field and velocity of the charge
Force is ______ to Velocity and the Magnetic Field
perpendicular
Since a force due magnetic field perpendicular to velocity, it does no ______
work
Magnetic Force changes the ______ but never the _____.
direction but never the magnitude
a changing magnetic field creates an _____. This process is non-conservative because mechanical energy is transferred into heat energy
electric field
Equation: circular path of charged particle through a magnetic field
q * V * B = m * (v^2 / r)
sin(90) = ?
= 1
cos(90) = ?
= 0
a moving charge experiences force when moving through a _______
magnetic field
a magnetic field is generated by ________
a moving charge
Equation: find circular path of a charged particle through a magnetic field
2 * pi (3.14) * r
Note: r = radius of circle
Equation: Magnetic Force
F = q * v * B
