chapter 2 Flashcards
loosely bonded electrons
atttraction between positive nucleus has on those electrons are small.
free elecrons experience an attraction to
neighbouring atoms
elements with free electrons are classed as
good conductors.
electron currrent flow
is from negative to posittive
conventional current flow
positive to negative. used in heavy currents.
conducter
substance through whic electric current can flow easily
electric current
movement of electrons through a specific substance in a specific direction.
potential difference
electricalpressure that causes current flow between twopoints in a circuit
emf
device that has the ability to maintain pd between two points in a circuit is said to develop emf.
devices that can develop emf
photo electric cell
electric cell or battery
electric generator
thermocouple
resistance
opposition offerred to flow of electric current.
resistor
device that has resistance as a chief property
insulator
prevent the flow of electric current
simple circuit needds the following:
.electric power device
.load such as a lamp
.two lengths of insulated conductors
.switch to open the continuous conducting path of circuit.
heating effect of an electric current
when flow of current is restricted there will be heat generated. since there is no perfect conductor there will alays be heat generated from all parts of the circuit. can be putto usex stove heater etc
power
it is the rate of doing work.
power is measured in
watts
where work is done energy is…
expanded
power formula
v x I
factors influencing the resistance of a conductor
.type of material {resistivity
.length of conductor in metres
.cross sectional area of conductor in m squared.
.tempersture of conductor.
resistivity
theresisting power of a specific material.
temperature coeeficccient of resistance
resistance of most materials are affected by changes in temperature.
positive temp coefficcient of resistancce
resistance of most materials increases when temperature of that substance increases.
negative temperature coeeficcient
resistance of of materials such as insulators pvc rubber , car batteries , carbon ddecreases with an increase in temperature.they are said to have a negative temperature coeffiecient of resistance.
alloys low coefficient of resistance
ALLOYS{MIXTURE OF ELEMENTS} USED FOR THE RESISTANCE WIRE OF ELEMENTS HAVE EVRY LOW TEMPERATURE COEFFICIENT OF RESISTANCE. THE RESISTANCE VARIES SO LITTLE THAT TEMPERATURE CANBE NEGELGTED.
3 EXAMPLES OF ALLOYS
EUREKA , MANGANIN , NICHROME
SIMPLEST CONTRIBUTING FACTOR THAT DETERMINES THE INTERNAL RESISTANCE OF A CELL IS
THE MATERIAL IT IS MADE OUT OF.
INTERRNAL REESISTANCE OF A CELL CAUSES INTERNAL
VOLT DROP WHILLE CURRENT IS FLOWING.
INTERNL VOLT DROPAGE CAUSES
TERMINAL VOLTAGE DROP.
when forming a battery , only
similar cells can be connected to form a battery
cells may be grouped in
series , paralelle or series parallel combinations.
since the emf of a single cell is low , they are often connected
in series.
when cells are connected in series , it increases
emf and also the internal resistance.
