ch22

a metal wire

can discharge the charge of a parallel-plate capacitator

• the wire will get hotter

• if the wire is thin → it can get hot enough to glow like in a lightbulb!

current

motion of charges through a material

charge carriers

carry charge in a current

• electrons in a metal

insulators

don’t have free charges so can’t carry a current

applying an electric field to a metal

exerts a force on the electrons so they accelerate

• collisions between electrons create warmth of the metal

electron’s average motion

opposite of the electric field

potential difference

creates the electric field to drive the current in the wire

current leaving =

current entering a lightbulb

• cannot destroy or store electrons

• conservation of charge

Law of Conservation of Current

current is the same at all points in a current-carrying wire

current

rate at which charge moves through a wire

Kirchhoff’s junction law

sum of in = sum of out

complete circuit

flow of charge in a continuous loop

charge escalator in a battery

sustains the current by providing a renewed supply of charges to the positive terminal

• powered by chemicals

established the potential differences between the terminals by separating charge

emf

electromotive force

• device that can actively cause charge separation to establish a potential difference

rating of a battery

emf

total potential difference of batteries in series

sum of voltages

potential difference causes a current

in the direction of decreasing potential

two factors determine current

• potential difference

• properties of the wire

current is proportional

to the potential difference

adding a second battery

increases the potential difference → increases electric field and current

resistance

increasing length of wire → decreases current

increasing thickness → increases current

resistivity

good conductors → low resistivity

poor conductors → high resistivity

ideal wire

resistance = 0

strength of electric field inside of a resistor

is uniform

Ohms law

R = V/I

as charge flows, the chemical energy of the battery dissipates into

thermal energy

increases resistance of a resistor

decreases the current

power dissipated in a resistor can be written with

any of the power equations