Charge (q)
Fundamental property of matter.
Comes from the protons and electrons in atoms.
Measured in Coulombs.
Only electrons are mobile.
Elementary Charge (qe)
Amount of charge on a proton (+) or electron (-).
All amounts of charge must exist in integer multiples of qe.
Law of Conservation of Charge
Amount of charged particles in the universe is constant.
Restatement of the Law of Conservation of Mass.
Charge cannot be created or destroyed, only transferred.
Charge Interactions
Similar charges repel.
Opposite charges attract.
Coulomb's Law
Describes the amount of force between any two charged particles.
The electrostatic force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Electric Field (E)
The field around charged particles that exerts a force on other charged particles.
Measured in N/C
Positive charges produce repulsive fields while negative charges produce attractive fields.
Fields of charges in the same area will affect each other.
Electrical Potential Energy (Ue)
The type of energy a charged particle has due to its interaction with an electric field (or other charged particle).
EPE increases when a charged particle moves where it "doesn't want" to go.
EPE decreases when a charged particle moves where it "wants" to
Electric Potential (V)
An energy value associated with a specific position within an electric field.
Isolines of electric potential run perpendicular to electric field lines.
It is a scalar, additive quantity for systems of point charges.
Potential Difference (?V)
Change in electric potential between two different locations.
Also referred to as "voltage"
Drives current through a circuit.
Measured in Volts
Electron Volt (eV)
The amount of energy an electron gains when accelerated across a potential difference of 1 volt.
A unit of energy more appropriate for small charged particles.
Capacitor
An electrical device used to store electrical charge.
Stores electrical energy in the UNIFORM electric field between its parallel conducting plates.
Current in a circuit STOPS when a capacitor is fully charged.
Current (I)
The rate at which charges move through a material.
I = q/t
Measured in Amps.
Conservation of Current
The current in a wire is the same everywhere in the wire.
Kirchhoff's Junction Rule
The sum of the currents coming into a junction must be equal to the sum of the currents leaving the junction.
Kirchhoff's Loop Rule
The change in electrical potential around any completed loop is zero.
Voltage is "gained" across batteries and is "lost" across resistors.
The resistors in a circuit must use all of the voltage provided by the battery.
Resistance (R)
The opposition the the flow of current through a material.
Determined by the physical characteristics of a material.
R = ?l/A
Measured in Ohms.
Ohm's Law
The current through a circuit is directly related to the potential difference.
The resistance of a resistor remains constant.
?V = IR
Resistors in Series
Current is the same everywhere in the circuit.
Voltage of the source is SHARED amongst resistors.
Resistors in Parallel
Current splits proportionally at junctions.
Voltage across separate loops is the SAME.
Short Circuit
A path of no resistance produces an extremely large current.
Item in the circuit are bypassed and will not function.
Electric Power (P)
The rate at which energy is used by the items in a circuit.
Related to the brightness of a light bulb.
Measured in Watts.
Capacitance (C)
The ratio of stored charge (Q) on the plates to the potential difference (?V) across the plates.
Fixed value determined by the physical characteristics of the capacitor.
Capacitors in Parallel
Voltage across capacitors is EQUAL.
Total charge stored is the sum.
Capacitors in Series
Voltage of the source is shared amongst capacitors.
Induced charge on each capacitor is EQUAL.
emf (?)
A pure or ideal source of potential difference (voltage)
Terminal Voltage
The actual resulting potential difference provided to the circuit by the source.
Is always less than the emf due to internal resistance.
Internal Resistance
Resistance within the power source that affects the total effective resistance of the circuit.
Modeled as an additional resistor connected in series.