Current Electricity Flashcards
what is current
the rate of flow of charge
what is potential difference/voltage
the energy transferred per unit charge between two points in a circuit
what is resistance
a measure of how difficult it is for charge to pass trough a component
what does ohm’s law state
that for an ohmic conductor current is directly proportional to the potential difference across it given that physical conditions are kept constant
what is an example of an ohmic conductor
a resistor
why does a diodes graph look like that
because it allows current to flow through easily one way but nit the other way so the potential difference and current is very low to begin with as the current cannot flow through easily due to the resistance
why does a filament lamp graph look like that
because it contains a metal wire which heats up so at the beginning as it is not very hit current can easily flow through as there is a low resistance how the hotter it gets the higher the resistance so it is more difficult for the current to flow through causing the gradient to decreased
what can we assume about ammeters and voltmeters resistance
ammeters have zero resistance and voltmeters have have infinite resistance so no current can flow through it so their measurement of potential difference across a component is exact
what is resistivity
is a measure of how easily a material conducts electricity
what does resistivity measure
is a measure of how easily a material conducts electricity
what will resistivity give the value of
the value of resistance through a material of length 1m and cross sectional area 1m^2
why is resistivity useful
because you can compare materials even though they might nit be the same size
what is resistivity also dependent on
environmental factors such as temperature
what will happen the resistance if the temp of a metal conductor increases
resistance also increases
why does the resistance increase if the temp of a metal conductor increases
because the atoms of the metal gain more kinetic energy and move more which causes the electron (charge carriers) to collide with the atoms more frequently causing them to slow down therefore current decreases and resistance increases
in a thermistor what happens to the resistance as the temp increases
the resistance decreases
why in a thermistor does resistance decrease when the temp increases
increasing the temp causes electrons to be emitted from atoms therefore the number of charge carriers increases and so current increases causing resistance to decrease
what is one application of a thermistor in a circuit
is a temperature sensor which can trigger an event to occur once the temp drops or reaches a certain value
what is a superconductor
is a material which below a certain temp known as the critical temp has zero resistivity
what does the critical temp of a superconductor depend on
the material it is made out of
which temp do most well known superconductors have a critical temp at
0K (-273 Degrees Celsius)
what are the applications of super conductors
- power cables which would reduce energy loss through heating to 0 during transmission
- strong magnetic fields which would not require a constant power source (could be used in maglev trains where there would be no friction between the train and the rail and in certain medical applications
how do you add resistances in a series circuit
Rt = R1 +R2 +R3 +….
how do you add resistances in a parallel circuit
1/Rt = 1/R1 + 1/R2 + 1/R3 + ….
