ELECTRICITY Flashcards
The greater the resistance across a component….
the smaller the current that flows( for a given potential difference across the component
CHARGE FLOW =
CURRENT* TIME
Q=IT
POTENTIAL DIFFERENCE =
CURRENT * RESISTANCE
V=IR
factors that affect resistance
length
if the circuit is in series or parallel
what type of resistance do ohmic conductors have
they have a constant resistance
Does the resistance of ohmic conductors change with current
No
when an ohmic conductor is at a constant temperature
the current flowing through it is directly proportional to the potential difference flowing through it
what is an LDR (2 points)
an LDR is an light dependent resistor that is dependent on the intensity of light.
what happens to the resistance of an LDR in bright light
the resistance falls
what happens to the resistance of an LDR in darkness
the resistance is highest
what can you use LDRs for
automatic night lights
outdoor lighting
burgular detectors
what is a thermistor
A thermistor is a temperature dependent resistor
what happens to the resistance of a thermistor in hot conditions
the resistance drops
what happens to the resistance of a thermistor in cool conditions
the resistance goes up
where can you use thermistors
they can be useful temperature detectors
car engine temp sensors
electronic thermostats
how are the components connected in a series circuit
the components are connected in a line, end to end between the power supply
the voltmeters in a series circuit are always connected in PARALLEL
what happens if you disconnect one component in a series circuit
the circuit is broken and they all stop
Potential difference is _________________ in a series circuit
the Potential difference is shared between the various components
potential difference in a series circuit will always add up to the __________
the source potential difference
Equation for potential difference connected in series
Vtotal= V1 + V2 + V3 …..
Current in a series circuit is ________
the same through all components
Equation for current connected in series
I1=I2=I3=I4
In a series circuit the total resistance of two components is the _______ of their resistances
sum
when a resistor is added to a series circuit what happens to the current and resistance
the total current is reduced and the resistance is increased
in a series circuit cell potential difference (V) ______
adds up
How are components connected in a parallel circuit
each component is connected separately to the power supply
What happens if you remove components in a parallel circuit
Hardly anything will happen to the cirucit
In a Parallel circuit Potential difference is ________
the same across all components
will identical bulbs connected in parallel be at the same brightness
yes because potential difference is the same across all components
In parallel circuits total current is ______________
is shared across the separate components
what does adding a resistor to a parallel circuit do to the resistance and the current
it decreases the resistance and it increases the current
What type of current is mains supply
AC current
What type of current is battery supply
DC current
how are alternating currents produced
they are produced by alternating voltages in which the negative and positive ends keep alternating
what voltage is the uk mains supply
230V
what is the frequency of the ac mains supply
50 Hz
what is dc current and how is it created
Direct current is current that is always flowing in the same direction
its created by direct voltage
Colour of live wire
brown
colour of neutral wire
blue
colour of earth wire
green and yellow
purpose of the live wire
provides the alternating potential difference at about 230V
purpose of neutral wire
the neutral wire completes the circuit and carries away current its around 0V
purpose of earth wire
it is for protection, it stops the appliance casing from becoming live its at 0V
when do earth wires carry current
when there is a fault
why can a live wire give you an electric shock
your body is at 0V this means that if you touch the live wire a large amount of potential difference is produced across your body and current flows through you. This causes an electric shock
can you still get an electric shock if the plug socket or switch is turned off
yes because there is still potential difference in the live wire, so if you make contact with the live wire your body would provide a link between the supply and the earth so current will flow through you.
equation for power in electrical appliances
ENERGY = POWER * TIME
E=PT
What does the power rating tell you
power rating tells you the amount of energy transferred between stores per second
the lower the power rating…
the less electricity an appliance uses in a given time so its cheaper to run
equation for energy transferred in a circuit
ENERGY= CHARGE FLOW*POTENTIAL DIFFERENCE
E=QV
Equation for power in an appliance
power= potential difference * current
p=VI
EQUATION FOR POWER WHCIH INVOLES CURRENT AND RESISTANCE
P=I2R
What does the national grid use ( pd and Current)
they use a high pd and low current
what do step up and step down transformers do
step up transformers increase the potential difference
step down transformers reduce the potential difference for domestic use
why is the national grid efficient at transferring energy
the national grid distributes electricity at a high pd and low current. a high pd means that it can distribute lots of power per second. using a low current reduces energy losses which makes the national grid efficient at transferring energy
Jake removes his jumper in a dark room he hears a crackling noise and sees tiny sparks between his jumper and his shirt explain
as the jumper rubs against the shirt a static charge builds up between the jumper and the shirt this is due to the electrons being removed from one and being deposited onto the other. The charge becomes large enough for electrons to jump across the small air gap between the jumper and the shirt causing sparks
what direction are the field lines on a positively charged isolated sphere
outwards
what direction are the field lines on a negatively charged isolated sphere
inwards
