B.5 Current and Circuits

q

Electric charge

unit of q

Coulombs

Charge is…

conserved & quantized

quantized means

made up of an integer multiple of a base unit

“free” electrons in a material make a…

conductor

no “free” electrons in a material makes a…

insulator

Potential difference definition

work done per unit charge to move a point charge from one point to another

V represents

potential difference

V units

Volts

Potential difference provided by a battery

EMF (electromotive force)

I stands for

Electric current

Electric current is…

rate of flow of charge through a cross section of a conductor

I unit

Ampere (A)

R stands for

Resistance

units of R

Ohms

Ohm’s law

R = V/I

Thermistor

temp-dependent resistors (^ temp, v resistance)

LDRs

light dependent resistors (^ intensity, v resistance)

Resistance of Ohm resistors depends on

material, wire length, cross-sectional area of the wire

rho is…

resistivity

method of measuring current

ammeter

method of measuring voltage

voltmeter

current behavior across resistors in series

remain equal

total resistance across resistors in series

sum of individual resistances

total voltage across resistors in series

sum of individual voltages

current behavior across resistors in parallel

sum of all currents (it splits)

voltage behavior across resistors in series

sum of individual voltages

kirchoff’s loop law

sigma V = 0

Kirchoff’s Current Law

sigma I in = sigma I out

total resistance of resistors in parallel

1/R = 1/R1 + 1/R2…

A real battery has…

internal resistance

Voltage in real batteries:

V = emf - Ir (r = resistivity)

Charging Definition

process of moving electrons form one place to another

3 types of charging

conduction, friction, induction

Charging by conduction occurs when…

an object with excess charge touches a neutral object

Charging by induction

bringing a charged object near a conductor

polarized

pos and neg charges on opposite sides of eachother

Electric field definition

force per unit charge experienced by a charge at a point

Electronvolt

Amount of work done when a charge equal to that of an electron is moved across a potential difference of 1V.

emf definition

amount of energy a cell transfers to each unit of charge

Current

Rate of flow of charge

resistance definition

measure of how difficult it is for current to pass through an electrcal component

resistivity def

property that measures how strongly it resists the flow of current

Ohms law

electric potential difference across a conductor is directly proportional to the current flowing through it, at constant temperature