electricity Flashcards
what is current
flow of an electrical charge
what is the unit of current
ampere A
what is potential difference
the driving force that pushes the charge
what is resistance
anything that slows the flow of charge down
what is the unit of potential difference
volt V
what is the unit for resistance
ohm
what is the equation of charge flow
charge flow = current * time
what is the equation for resistance
PD = current * resistance
what graph does a ohmic conductor create and why
current is directly proportional to PD so you get a linear graph
what graph does a filament lamp create and why
as current increases the temp of the lamp does so resistance increases
what graph does a diode create and why
current only flows in one direction. has high resistance in reverse
how does resistance effect an LDR
dependent on light intensity
bright light resistance falls and in dark resistance is highest
how does resistance effect a thermistor
dependent on temp
hot resistance falls and when cold resistance increases
what is a series circuit
components connected in a line
potential difference in a series circuit
is shared
current in a series circuit
the same
resistance in a series circuit
adds up
what is a parallel circuit
components is seperatly connected
potential difference in a parallel circuit
the same
current in a parallel circuit
shared
resistance in a parallel circuit
reduces the total resistance if you add resistor
what is AC
current constantly changing direction
what is the frequency and PD of AC
50 Hz and 230 V
what is the live wire and it’s coulor
provides the AC and is brown
what is the neutral wire and it’s coulor
completes the current and carries away current and is blue
what is the earth wire and it’s color
protects the wiring and for safety and is green
what are electrical appliances meant to do
transfer energy to components in the circuit when a current flows
what is the power of an appliance
energy that is transferred per second
equation for energy transferred
power * time
what is the power rating
tells you the maximum amount of energy transferred between stores per second
what does the power rating tell you
the lower the rating the less electricity it needs and so its cheaper to run
an appliance may be more powerful but it can have less efficiency meaning it could transfer the same amount of energy to useful stores
what happens when charge goes through a change in PD
energy is transferred
equation for energy transferred in terms of charge
charge flow * PD
equation for power
PD * current
what is the national grid
a giant system of cables and transformers that cover the uk
how do power stations meet demand
run below the maximum power out put so there is spare capacity
when is demand the most
the morning and night
why does the national grid use a high PD
increasing the PD decrease the current which decreases energy lost to the environment
why does the national grid use a low current
a high current would use loads of energy as the wires heat up and energy is transferred to the surroundings
how do transformers work on the national grid
transformers step up the PD at one end and then bring it down to a safe level
how does the earth wire work
wire is connected to case and ground
as the wire is copper there is low resistance allowing the current to follow the path to the ground reducing risk
what does a fuse do
melts if the current is too high
how does a fuse work
if the case becomes live the large current will flow through the earth wire and melt the fuse
how how does static cause sparks
as electrical charge builds up the PD between object and earth increases allowing electrons to jump across to the object or earthed conductor
how does static work
insulating materials are rubbed, negatively charged electrons will be scraped off one and dumped on the other
what are electric fields
created around any electrically charged object
how sparking works
a high PD causes a strong electric field between the charged object and earthed object
the field causes electrons in the air to be removed (ionized)
when air is inozed it is more conductive so a current flows
interaction of charged objects
electric fields of each object interact causing attraction or repulsion
as you increase the distance of the objects the strength of the field decrease and the force is smaller
