Electricity Flashcards
(17 cards)
what’s ohms law
it’s how current could change as the applied pd increases cor certain types of conductors
why isn’t semi conductors good at conducting electricity like metals
because they have fewer charge carriers available
what are two semiconductors
thermistors and diodes
what’s a thermistor
it’s a resistor with a resistance that depends on temperature
NTC thermistors (negative temp coefficient)
the resistance decreases as temp goes up
explain what happens to a thermistor in the graph
as the current increases it increases temperature
the increasing gradient shows that the resistance is decreasing
what are diodes
they’re designed to let current flow in one direction only
it requires a threshold voltage of 0.6 V before it will conduct
in reference to charge carriers how does an NTC thermistor connected to a circuit can be used as a temp sensor
as the temp of thermistor increases, more charge carriers are released,
more charge carriers available allows more current to flow in the circuit
so the current in the circuit can be used to monitor temperature
what are the three things that determine resistance
length ( the longer the more discount it is to make current flow)
area ( the wider it is the easier it will be for electrons to pass)
resistivity ( depends on material and factors like temp and light intensity)
how it resistivity defined
it’s defined as the resistance of a 1m length with 1m2 cross sectional area measured in ohm meters
why do super conductors have zero resistivity
because the temp is below critical temp
so none of the energy turns into heat so current will flow forever
what’s some uses of super conductors
power cables that transmit electricity without any loss of power
strong electromagnets that don’t need a constant power source
electronic circuits that work really fast because there’s no resistance slows them down
what’s kirchhoffs first law
the total current entering a junction = the total current leaving it
in electrical circuits when is the charge emf and when is it pd
when energy transferred to a charge it’s emf
when energy is transferred from a charge it’s pd
what’s kirchhoffs second law
the total emf around a series circuit equals the sum of the pd across each component
how does an LDR work with resistance
if it’s in the dark it has HIGH resistance
if it’s in the light it has lowww resistance
what’s internal resistance
it’s the lost volts per unit current
what happens to the voltmeter reading as light intensity decreases
when light intensity decreases the total resistance increases
and since the resistance increases the current decreases
and as v= IR the resistance is fixed and the current decreases soooooo
voltage across decreases
but voltage in LDR increases because of kirchhoffs 2nd law so the voltages add up to the Emf
