Current & Resistance
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current
rate at which charges move through cross section of wire or given medium; movement of electric charge

SI unit for current
1 ampere A = 1 coulomb/sec c/s

charge carriers
positive or negative charges in motion

conventional current
 current consisting of positive charges that goes in direction of electric field, from positive to negative
 represents the effect of the actual motion of the charge carriers (equivalent conventional current of negative is in opposite direction; same direction for positive)

drift velocity
net velocity of the charge carrier moving in an electric field, taking all of their collisions and zig zags into account

how a current is created
 potential difference is applied across conductor
 charge carriers have to be "pumped" through the circuit; work has to be done on them to maintain v
 electric field force sets the electrons in movement
 charges collide with atoms in the device and convert electrical potential energy to kinetic energy to move

how batteries/generators maintain a potential difference
they convert energy into electrical energy, this energy is supplied to charge carriers

energy conversion in batteries vs. generators
 batteries convert chemical energy to electrical energy
 generators convert mechanical energy to electrical energy

direct current
 charges move only in one direction, potential difference is fixed
 generated by batteries and generators

alternating current
 terminals of the source of the electrical potential are always changing signs, no net motion
 only generated by generators

point of conductor
surface perpendicular to the motion of the charges

circuit
charge flows through a closed path and returns to its starting point

power
rate at which work is done; rate of energy transfer

power of a resistor
amount of heat produced when current flows through (joule heating: heating of the resistor)

electromotive force emf
max potential difference of a device

terminal voltage
 actual potential difference between the terminals
 less than the emf because of the internal resistance of the battery (caused by collisions between charges and atoms within battery)

resistance
opposition of the motion of charge through a conductor, quantified by the geometric characteristics of the material through which the charge is moving

resistance SI unit
1 ohm = 1v/amp

resisitivity and temperature relationship
 usually resistivity and temperature increase together
 for semiconductors, there is an inverse relationship

Ohm's Law
 ratio of a potential difference applied across a conductor to the current through the conductor is constant
 graph of current vs. potential difference is linear with a constant slope equal to the inverse of the resistance

ohmic
materials that follow Ohm's Law; constant resistance over a wide range of potential differences

potential difference and current relationship
 higher potential difference means greater current
 directly related

length effect on resistance
shorter objects have less resistance; longer objects have greater resistance

crosssectional area effect on resistance
greater area has less resistance; smaller area has greater resistance

temperature effect on resistance
lower temperatures have less resistance; higher temperatures have more resistance

relationship between current and resistance with constant potential difference
inverse relationship; current decreases when resistance increases

short circuit
 has very little resistance so more energy gets dissipated, lacks a resistor
 usually the circuit is cut off from a capacitator so recharging does not occur; burns out quickly
 low resistance increases current, can cause circuit to overheat and catch fire

series circuit
provide a single conducting path without junction; only one path for the charge to follow

parallel circuit
connected with junctions providing separate conducting paths; some charged go one way, others go the other

schematic diagram
graphic representation of an electric circuit with symbols representing circuit components

electric circuit
path through which charges can be conducted; set of electrical components connected so that they provide complete paths for charge movements

load
element that dissipates energy, increases the resistance and is a type of resistor (e.g. light bulb)

simple circuit
has a source of potential difference and electrical energy (e.g. battery) and a load (e.g. light bulb)

closed circuit
closedloop path for electrons to follow, path from one battery terminal to the other is complete, switch is closed to allow steady current flow

open circuit
incomplete path and no charge flow and no current, switch is open, circuit does not work

potential difference across a load and terminal voltage
 potential difference across a load equals the terminal voltage
 conservation of energy says that the energy gained must equal the energy dissipated in a charge's trip in a circuit

watt conversion
1 w= 1 vxa

battery drawing
  longer side is positive, shorter side is negative

relationship between parallel and series circuit
inversely proportional

equivalent resistance
 a single resistor can replace a group of series or parallel resistors; represents total current found by using individual resistance values
 for series circuits, add the sum of the individual resistances
 for parallel circuits, do the same with inverses

current in series/parallel circuits
 constant throughout series circuits (conservation of charge, current is the same throughout all resistors)
 proportioned across each resistor in parallel circuits

voltage in series/parallel circuits
 proportioned across each resistor in series circuit
 constant throughout each resistor in parallel circuits (sides of bulbs are connected to common points, so voltage across is the same)

do series/parallel circuits require all elements to conduct?
 series require all elements to conduct
 parallel do not require all elements to conduct; provides separate alternate pathways

relationship between equivalent resistance and individual resistances in parallel circuits
inversely related; low equivalent resistance can be created with a group of high resistances in parallel

complex circuits
consist of series and parallel circuits