P2 Electricity Flashcards
battery
two or more cells
current
measure of the flow of electrons around the circuit
current measured in
amps (A)
potential difference is the force driving the flow of
electrons
potential difference is provided by the
cell/battery
potential difference is measure in
Volts (V)
resistance is
everything that resists or opposes the flow of electrons around
resistance is measured in
Ohms (Ω)
current always flows from
positive terminal to negative terminal (even though it makes no sense)
what is ohm’s law
v = i x r
so long as resistance remains constant, potential difference and current are…
directly proportional
on current/potential difference graphs, the greater the resistance =
the less steep the gradient
temperature increase=
resistance increase
what does current increase result in on IV characteristics graph
current increase = increase heat = increase resistance = gradient less steep
diodes only allow current to flow
in one direction
diodes only show current when potential difference is
positive
what do diodes have in the opposite direction so that no current can flow?
really high resistance
charge is
a measure of the total current that flows within a certain period of time
charge is measured in
coulombs (C)
what happens if a component breaks in a series circuit?
the whole circuit stops working
how is the potential difference shared in a series circuit
across all components
in series circuits, Vtotal =
V1 + V2 + V3…
How is current shared in series circuits?
Current is the same everywhere
Current is measured by an
Ammeter
Ammeters are placed
in series
why can ammeters be placed anywhere in series circuit
because current is the same everywhere
in series circuits, total resistance =
sum of resistance of each component
voltage of single component =
current x resistance of component
what are volts measured by
voltmeter
voltmeters are connected in
parallel to the component you are looking at
components with greater resistance always have
a higher share of the voltage
parallel circuits are circuits with
more than 1 loop
in parallel circuits, if a component breaks
the overall circuit is still in tact
in parallel circuits, the potential difference of components are always the same as the total
Vtotal = V1 = V2 = V3
in parallel circuits, the sum of each loops current
adds to the total current that flows
In parallel circuits, Itotal =
I1+I2+I3…
In parallel circuits, loops that have greater resistance
take a lower share of the current
electrical current takes the
path of least resistance
more components in parallel=
lower total resistance
most power stations generate thermal energy and convert it into
electrical energy
power stations often run way below maximum capacity in order to
cope if demand skyrockets
power is measured in
Watts (W)
why is high current an issue for the transmition of electrical power through the national grid?
high current = lots of heat, resulting in a lot of energy lost to thermal store
why is voltage so high on the national grid?
p = v x i and current has to be really low, so voltage must be really high to still have high power output
what do step-up transformers do?
increase voltage to 400,000V
what do pylons do?
transmit electricity across the country
what do step-down transformers do?
reduce voltage to safe levels before electricity reaches towns and cities
what is alternating current (AC)
when the direction of current often swaps back and fortn
when does alternate current occur?
when potential difference fluctuates between positive and negative
what current is mains supply
alternating current
mains supply alternates between…
at a rate of…
+230V and -230V at a rate of 50Hz
direct current remains
either positive or negative the whole time
whit direct current, charge is always
flowing in the same direction
what displays AC and DC graphs on a monitor
oscilloscopes
what colour is the live wire?
brown
what colour is neutral wire?
blue
what colour is earth wire?
striped green and yellow
what are wires in mains supply made of and why?
copper to conduct electricity
what must copper wires in mains supply be coated in and why
insulating plastic for safety
what does the live wire do?
provides alternating potential difference of 230V
what does neutral wire do?
carries away current
in terms of the live and neutral wire, what does potential difference do?
flows in through live wire and out through neutral wire
in the neutral wire, what potential difference is electricity?
0V
what potential difference does earth wire have?
0V
what is the purpose of earth wire?
safety: if the live wire comes into contact with the appliance casing, the earth wire stops the casing from having a high voltage by providing an alternate pathway for current to flow
difference in voltage causes
electricity to pass from one to the other
electricity passes from
high voltage to low voltage
why do humans get electrocuted if they touch the live wire?
the live wire has a voltage of 230V and humans have a voltage of 0V, electricity moves from high voltage to the low voltage
What sort of resistance do conductors have
very low resistance
total resistance of resistors in parallel
is less than the resistance of the smallest resistor
mA = milliAmps:
divide by 1000 to get Amps
MA = megaAmps:
times by 1,000,000 to get amps
