Electricity Flashcards
current
the rate of flow of charge
which way does conventional current flow?
positive to negative
which way does electrons flow?
negative to positive
mean drift velocity
average distance travelled by a charge carrier per unit time
charge carrier
something which caries charge (electrons and ions)
what does charge carrier density determine?
whether a material is a conductor, insulator or semiconductor
represented by n
kirchoffs first law
the total current entering a junction is equal to the total current leaving a junction (conservation of charge)
what is the link between current and charge carrier density? and resistivity?
the ability to carry a current increases with an increase in charge carrier density
the resistivity of a material is directly proportional to charge carrier density
what is an anode?
positively charged electrode
what is a cathode?
a negatively charged electrode
what is a cation?
positively charged ions
what is an anion?
negatively charged ions
electric charge
a measure of how charged an object is
(measured in coulombs)
quantised
a unit that can only be a certain value
eg. charge will always be a multiple of 1.6x10^-19
electrolytes
liquids that can carry an electric current
conductors
materials that have a high charge carrier density
semiconductors
materials that have an intermediate charge carrier density
it also has a conductivity between a conductor and insulator (dependent on temperature)
insulators
materials that have a low charge carrier density
potential difference
the energy transferred per coulomb of charge
the work done per coulomb of charge that passes between two points
electromotive forces
energy supplied per coulomb of charge
the amount of chemical energy converted to electrical energy per coulomb of charge when passing through a power supply
thermionic emission
the emission of electrons through the action of heating
resistance
a measure of how much a component resists the flow of charge
ohms law
potential difference is directly proportional to current
how do you work out the resistance of resistors in series?
add them together
how do you work out the resistance of resistors in parallel?
1/total resistance= 1/R1+ 1/R2 +…
resistance
how much an object opposes the flow of current
what factors affect resistance?
length
cross sectional area
material
temperature
resistivity
a measure of how strongly a material opposes the flow of electric current
conductivity
The degree to which a specified material conducts electricity (S/m)
conductance
The degree to which an object conducts electricity (S)
IV characteristics of a fixed resistor
-voltage is proportional to current
-ohmic conductor
-resistance is constant
-behaves the same regardless of polarity
IV characteristics of a filament lamp
-voltage is not proportional to current
-non-ohmic conductor
-resistance isn’t constant
-behaves the same regardless of polarity
-s shape on a graph
IV characteristics of a diode
-voltage is not proportional to current
-non-ohmic conductor
-resistance isn’t constant
-behaviour dependent on polarity
-backwards l shape
negative temperature coefficient
as temperature increases resistance decreases
(in some semiconductors as temperature increases so does the charge carrier density)
thermistor
as temperature increases resistance decreases (ntc)
Fundamental frequency
The lowest frequency that can fit
Kirchoff’s second law
The directed sum of the potential differences (voltages) around any closed loop is zero
