electricity Flashcards
what are the simple symbols in a circuit and what do they do
battery - providing electric power
filament lamp - bulbs
fuses - break if too much current flows through the circuit
switch - allows electricity to flow
diodes - only allow current to flow in one direction
light emitting diodes - allow light when current flows the correct direction through a circuit
what do ammeters measure
current
what do voltmeters measure
potential difference
what is a fixed resistor
provides a certain amount of resistance
what is a variable resistor
modify the amount of resistance
what are light dependent resistors
resistance is dependent on the intensity of light
the brighter - lower resistance
the darker - higher resistance
what are thermistors
resistance is dependent on the temperature
the hotter - resistance falls
the colder - resistance rises
what is potential difference
the force which drives the flow of electrons
(V)
what is current
measure of the flow of electrons around a circuit (I)
what is resistance
everything that resists/ slows the flow of electrons
which way does a circuit flow
current always flows from the positive terminal to the negative terminal. with the positive being the right battery
what is electrical charge
flow of negatively charged particles that transfer electrical energy from a cell/battery through conducting wires as an electrical current
what is a series circuit and what would happen if one component stopped working
a single loop circuit - the whole circuit would stop working
how is potential difference shared in a series circuit
shared across the whole circuit
as such
V total = V1 + V2 + V3
how is current shared in a series circuit
it is the same everywhere around the circuit
how do you find the total resistence in a series circuit
the sum of the individual resistence of each component.
what is a parallel circuit and what would happen if one component would stop working
a circuit with multiple loops - the rest of the circuit would still work
how is potential difference shared in a parallel circuit
the potential difference of the whole circuit is the same as each component because charge can only pass through any one branch
how is current shared in a parallel circuit
sharded between each of the branches
total current = the sum of current through each branch
what is different about the resistence in a parallel circuit
the more components in a parallel circuit the lower the resistence
what is alternating current
the direction of current flows in both directions
why does alternating current occur and when is it used
this happens when we use an alternating potential difference
- mains electricity
draw a potential difference/voltage/ current and time graph for an alternating current
potential difference - side
time - bottom
line fluctuating from -240 to +240
( the mains supply in the UK is 240 vaults ad 50Hz
how would you describe an alternating current graph
fluctuating
what is direct current
the direction of current flows in one way. either negative or positive not both
when is direct current used
cells and batteries
draw a potential difference/voltage and time graph for a direct current
voltage on side
time on bottom
line either negative or positive
how do we get potential difference/ time graphs
oscilloscope
what are some important facts about mains electricity
- alternating current of 240 vaults
- 50Hz
- provided by the national grid
how is the main electricity delivered to our houses
plugs
what are the different wires in a plug
live wire, neutral wire, earth wire
explain the live wire
-brown
-provides alternating potential difference from the mains
-electricity flows in through this wire
-240V
explain the neutral wire
- blue
- completing the circuit by carrying away current
- electricity flows out through this wire
- 0V
explain the earth wire
- green/yellow
- no current
- stops the appliance casing from becoming live
- prevents electric shock
what happens if you touch the live wire
large amount of potential difference (240V) flows through our bodies which has a potential difference of 0V causing an electric current
what is power
the energy transferred per second
what is the equation which includes power, time and energy transferred
E=Pt
energy transferred= power x time
what is the equation which includes energy transferred, charge and potential deference
E=QV
energy transferred= charge x potential difference
what are some examples of appliances that transfer electrical energy to kinetic energy
blenders and fans
what are some examples of appliances that transfer electrical energy to thermal energy
irons and kettles
what appliances transfer electrical energy to both thermal and kinetic energy
hairdryers and washing machines
what is the rate of power
1W = 1 J per second
which appliances have a higher rate of power
those designed to generate thermal energy
what is the network called that spreads across the UK to generate electricity
the national grid
where is electricity generated and what is this transferred into in order to be be spread around Uk
power stations, this is generated as thermal energy (from fossil fuels) and transferred into electrical energy
what does the national grid need to transmit loads of and why is this a problem
power
- to get high power you need high voltage and current but high current causes a lot of heat which would be lost to the surroundings.
what can you do to stop loosing electricity to the surroundings
keep the current low and voltage to be increased
how can you increase the voltage and how much does this increase it to
use a step up transformer
- 400, 000 v
what happens in the national grid after it has passed through a step up transformer
wires then transmit this electricity round the country between pylons. the voltage is then lowered to around 240V before it is entered into house mains
what is static charge
the build up of charge on insulating materials
why are materials normally mutual
they contain positive and negative charge and therefore cancel out
what happens if materials are rubbed together
the friction causes the electrons to rub off of one and onto the other
why does charge not build up with conducting materials
because the electrons are able to move, they can flow back to the other object
what happens when two insulating materials are rubbed together
the electrons can’t flow back and so the transfer of electrons because of the friction gives a positive static charge to the material that lost the electrons and a negative charge to the material gaining the electrons ( this positive and negative charge depends on the materials used)
what happens if an object keeps gaining negative electrons
as the size of the charge increases a potential difference will develop between the material and the earth/ any earthed object (humans) because they have a voltage of 0. if the potential difference between the charged object and earth is large enough it will cause a spark
because electrons will have jumped across the gap
what is an electric field
a region around a charged particle or object within which a force would be exerted on other charged particles or objects
how do you draw an electric field
positive - away
negative - toward
use field lines
where is the electric field strongest
the closer to the particle the stronger the electric feild
what happens if two opposite charged partials are close together
two of the same charged?
there will be an attractive force
( electrostatic attraction)
they would repel each other
how can you show an electrostatic attraction on a diagram
use the field lines by extending them from the positive particle to the negative particle
how is there a reaction between electric fields and air and what does this cause
if there is a strongly charged object it can cause the surrounding air particles to loose electrons and become positively charged ions (ionisation) . the air is then able to conduct electricity allowing sparks to travel through the air
