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considered the flow of positive charge even though only negative charges are actually moving


metallic conductivity

solid metals and molten forms of some salts


electrolytic conductivity

seen in solutions



reciprocal of resistance, property we will examine in detail later


SI unit for conductance

siemens (S) sometimes given as siemens per meter (S/m) for conductivity


metallic bond

an equal distribution of charge density of free electrons across all of the neutral atoms within the metallic mass


how to measure conductivity of electrolyte solution

place solution as a resistor in a circuit and measure changes in voltage across the solution


electrical current

the flow of charge between two points at different electrical potentials connected by a conductor (such as copper wire)


magnitude of current

I(i) = Q/change in t; amount of charge Q passing through the conductor per unit time


SI unit of current

ampere (1 A = 1 C/s)


how would positive charge flow if it flowed (direction of current)

from higher electrical potential to lower potential


direct current

tested to exclusion of alternating current (AC) on mcat; charge flows in one direction only


potential difference (voltage)

produced by electric generator, galvanic (voltaic) cell, a group of cells wired into a battery, etc.


electromotive force (emf or epsilon)

when no charge is moving between the two terminals of a cell that are at different potential values; not actually a force but is a potential difference measured in joules per coulomb (1 V = 1 J/C)


Kirchhoff's junction rule

at any point or junction in a circuit, the sum of currents directed into that point equals the sum of currents directed away from that point; expressed as I (sub into junction) = I (sub leaving junction)


Kirchhoff's loop rule

around any closed circuit loop, the sum of voltage sources will always be equal to the sum of voltage (potential) drops; V (sub source) = V (sub drop)
true of closed loops and not necessarily entire circuits



opposition within any material to the movement and flow of charge; insulators have very high resistance; conductors have very low resistance



conductive materials that offer amounts of resistance between that provided by conductors and insulators; dependent on characteristics of it like resistivity, length, cross-sectional area, and temp.


equation for resistance

R = (fancy p x L)/A fancy p = resistivity, L = length of the resister, A = cross-sectional area



intrinsic resistance to current flow in a material represented by fancy p; SI unit is ohm-meter (omega x m)


Length of resistor

resistance is directly proportional to length of resistor; longer means electrons will have to travel greater distance through a resistant material; if resistor doubles in length, resistance will also double


Cross-sectional area of resistors

inverse proportionality to resistance; if cross-sectional area is doubled, resistance is cut in half increasing number of conduction pathways


Temperature of resistors

most conductors have greater resistance at higher temps due to increased thermal oscillation of the atoms in the conductive material which produces greater resistance to electron flow


Ohm's Law

states that for a given magnitude of resistance, the voltage drop across the resistor will be proportional to the magnitude of the current. And for a given resistance, the magnitude of the current will be proportional to the magnitude of the emf (voltage) impressed upon the circuit. V = IR where V = voltage drop, I is the current and R is the magnitude of the resistance measured in ohms (omega symbol)


actual voltage supplied by a cell to a circuit due to internal resistance

it is less: V = E sub cell - ir sub int where V is the voltage provided by the cell, E sub cell is the emf of the cell, i is the current through the cell and r sub int is its internal resistance


internal resistance

there is a measure of internal resistance by every conductor; if the cell is not actually driving any current the internal resistance is 0 and voltage of cell is = to emf. If not zero, then voltage is less than emf


secondary batteries

certain type of power cells that can be recharged by an external voltage applied in such a way to drive current toward the positive end of the secondary battery rather than the typical of moving from the positive (higher potential) end to the negative (lower potential) end; acts as galvanic cell when discharging and electrolytic cell when recharging


Power equation

ratio of work (energy expenditure) to time: P = W/t = delta E/t


equation for rate at which energy is dissipated by a resistor

= the power of a resistor: P = IV = I^2R = V^2/R; I = current through resistor; V = voltage drop across resistor; R = resistance of resistor



one of two ways in which resistors can be connected into a circuit, all current must pass sequentially through each resistor connected in a linear arrangement