electricity Flashcards
what is a circuit
a closed loop that contains a power source and something for electrons to flow through
what is current and what is it measured in
a measure of the flow of electrons around the circuit, it is measured in amperes
what is potential difference/voltage and what is it measured in
force driving the flow of electrons and is provided by a cell or battery, measured in voltage
what is resistance and what is it measured in
everything that resists or opposes the flow of electrons, it is measured in ohms
which way does a circuit current flow
from the negative terminal to the positive terminal, in our exams it is from positive to negative (conventional current)
what is the equation for potential difference
V = IR
potential difference = current x resistance
what happens to resistance when you increase temperature
when temperature increases so does resistance
what is charge
a measure of the total current that flowed within a certain period of time
what is charge measured in
coulombs (C)
what is the equation for charge
Q = I x t charge = current x time
what does a fuse do
break if too much current flows through the circuit (used for safety)
what does a diode do
only allows current to flow in one direction
what does an ammeter do and how is it connected to the circuit
measures current and is connected in series
what does a voltmeter do and how is it connected
measures the voltage and is connected in parallel
what does a resistor do
it restricts the flow of electric current
what is an light-dependent resistor
a resistor which resistance is dependent of the intensity of light
what is a thermistor
a resistor which is dependent on temperature
what is a series circuit
a circuit which only has a single loop
what is a parallel circuit
a circuit that has more than one loop
what happens if a component is damaged or removed in a series circuit
the whole circuit will stop working
what is the potential difference like across a series circuit
it is shared across all of the components
what is current like across the circuit
current is the same everywhere across the circuit
what is resistance like across a series circuit
different components might have different resistances and the total resistance is the sum of all of the different resistances
why are parallel circuits usually more useful than series circuits
if one component breaks, the overall circuit is still intact
what is voltage like across a parallel circuit
all components get the full source of potential difference
what is current like across a parallel circuit
current is shared across the the parallel circuit, loops might have different currents
what is resistance like across a parallel circuit
more components in parallel = lower total resistance
what is the national gird
the national grid is the network of cables and transformers that transport electricity from the power stations to our homes, factories, offices, shops and other places that require it
how do power stations work
by generating a lot of heat and then converting that into electrical energy
how do power stations cope with surges in demand for energy
the have spare capacity and often run below their maximum power output
why is the current kept low across the national grid
high current means lots of energy will be lost as heat to the surrounding so the current has to be kept low while the voltage is very high
what do step-up transformers
the increase the voltage to 400,000 V
what do step-down transformers do
decrease the voltage to 230 V so it is safe for our homes and buildings
what is the formula for power
power = voltage x current power = current^2 x resistance
what are the two types of current
- alternating current (A.C)
- direct current (D.C)
what are the two types of current
- alternating current (A.C)
- direct current (D.C)
how does the charge flow in an alternating current
it is always changing direction
give an example of A.C
mains supply is A.C
what is the voltage of mains supple
230 V
what is the frequency of mains supply
50 Hz
what is direct current produced by and how does it flow
it is produced by a direct potential difference and is either negative or positive the entire time, therefore the charge is always flowing in the same direction
what is direct current produced by and how does it flow
it is produced by a direct potential difference and is either negative or positive the entire time, therefore the charge is always flowing in the same direction
give an example of D.C
cells/batteries
what is an oscilloscopes
devices from which we can get potential difference vs time graphs
what is a 3-core cable
a cable with 3 wires inside of it
what are the different wires in a three-core cable
- live
- neutral
- earth
what are the wires in a 3-core cable made from
copper as it in a good conductor and it is coated in a layer os insulating plastic
what colour is the live wire and what does it do
- brown
- provides the alternating potential difference from the mains
what colour is the live wire and what does it do
- brown
- provides the alternating potential difference from the mains
- 230 V
what colour is the neutral wire and what does it do
- blue
- completes the circuit by carrying away current
- effectively electricity flows out of the neutral wire
- 0 V
what colour is the earth wire and what does it do
- green and yellow
- 0 V
- doesn’t normally carry a current
- stops the appliance casing from becoming live
what colour is the earth wire and what does it do
- green and yellow
- 0 V
- doesn’t normally carry a current
- stops the appliance casing from becoming live
- provides an alternative pathways for the electricity to pass through
what happens if humans touch the live wire
it will create a large current to flow in the form of an electric shock
what is a surge
a sudden increase in current
what is a fuse (not in a circuit)
a very thin piece of wire
- which will melt and break the circuit if there is a surge
what is the advantages and disadvantages of fuses
- simple and cheap
- but they are permanently broken after a single surge
what is a circuit breaker
break the circuit when there is a surge
- they aren’t permanently damaged and only trip to turn of the circuit
- can be reset
what is earthing
if the live wire is touching the casing the earth wire will provide an alternate pathway for the current so that we don’t get an electric shock
what is double insulation
covering the entire appliance in a plastic casing so that no metal is exposed
what is static electricity
build up of charge on insulating materials
how does friction transfer electrons
rubbing two objects together means electrons will rub off of one object to another and cannot flow back as they are insulating materials
what happens when an object gains too many electrons
a potential difference is developed with the charged material and any earthed object
- if the pd is great enough electrons can jump across the gap
- this creates a spark
how are electric fields represented in physics
in field lines that go from positive to negative
describe the strength of an electric field
it is the strongest close to the particle and gets weaker the further away you get
what is ionisation
when a strong electric field causes air particles to lose their electrons and conduct electrify
- this is how sparks can travel
