electricity test revision Flashcards
topics: - Direct and alternating potential difference - Mains electricity and the national grid - Power and energy transfers - Different energy sources - Circuit diagrams - Electric components
The role of an oscilloscope is to what?
Display how voltage changes with time
what’s an oscilloscope?
it’s a device that produces and displays potential difference first time graphs on the monitor, showing the change of voltage with time
what is an Alternating current is caused by?
this is caused whenever we use an alternating potential difference which causes the current to periodically change direction.
what is an Direct current is caused by?
caused by a constant flow of electrons in one direction, typically produced by sources like batteries or cells.
All countries use alternating current as their mains supply.
In the UK, the mains supply has a frequency and voltage of what
Frequency = 50Hz
Voltage = 230 V - 240 V
this means that the potential difference fluctuates from
240v to -240v 50 times per second
what an Alternating current?
it’s a current that changes direction repeatedly
(constantly swapping back and fourth)
meaning it fluctuates between positive and negative
It is supplied by mains electricity.
e.g. plug sockets , powers computers/ kettles etc…
what a Direct current?
it’s a current that is always flowing in one/same direction only.
meaning it’s either negative or positive (only one)
It is supplied by cells or batteries.
Electricity demand varies during the day and generally peaks when?
the afternoon
as that’s when people come back from school/work.
time where people would cook food or watch tv and play games
The formula for electric power is?
the other one
power = voltage × current
what is the symbol formula for electric power?
P = IV
* v = potential difference
* I = electric current
what does High currents effect the wire?
High currents cause the wire to heat up, meaning that energy is lost as heat to the surroundings.
Step-up transformers are used for what?
Increase the voltage and decrease the current
Step-down transformers are used for what?
Decrease the voltage and increase the current
How electric power gets to our homes (simple 5 points)
Electric power is generated at a power station.
Step up transformers increase the voltage and decrease the current.
The electric power is transmitted via the national grid at low current which minimises power loss.
Step down transformers decrease the voltage and increase the current near our homes.
Electric power is wired into our homes at a voltage that is relatively safe to use.
where does most of our electricity come from and how?
power stations.
They generate loads of heat through:
- Burning fuels: Fossil fuels like coal, oil, or gas.
- Nuclear reactions: Using nuclear fission to release energy.
- Geothermal energy: Heat from the Earth’s interior.
This heat is used to produce steam, which drives turbines. The turbines then spin generators, converting thermal energy into electrical energy.
How do power stations handle surges in electricity demand?
Power stations usually operate with spare capacity, meaning they run below their maximum power output. This allows them to quickly increase electricity production to meet surges in demand.
A power source for an electric circuit could be a…
Cell
Battery
Current
‘I’
a measure of the flow of electrons around a circuit
similar like the flow of water
Amps (A)
Potential difference
‘v’
Potential difference is the force driving the flow of electrons around a circuit
like the pump that forces the water along the pipe
also known as ‘Voltage’
MEASURED IN ‘V’
In ‘conventional current’, we say that the electrons flow from
Positive terminal ➔ negative terminal
Resistance
‘R’
Resistance is everything that resists or opposes the flow of electrons in a circuit
similar to a plug blocking the water flow
measure in Ohms (Ω)
For wires and resistors, increasing the temperature will __________ the resistance.
increase
As temperature increases, all of the ions in the metal vibrate faster, which makes it harder for electrons to pass along the wire (or in other words, the resistance increases).
Diodes
Only allow current to flow one way around a circuit
charge
‘Q’
a measure of the total currents that flowed within a certain period of time
measured in coulombs (C)
charge in an water analogy
charge could be the total amount of water that has flowed down the hill within a certain time
formula for charge
charge = current × time
The units for charge are
Coulombs (C)
The symbol formula for charge
Q= It
A light emitting diode will…
Only allow current to flow in one direction
Emit light when current flows through it
ammeters
- They are added to a circuit in series
- They measure current
A resistor whose resistance decreases when temperature increases is a…
Thermistor
Which of the following statements about voltmeters are true?
They measure potential difference
They are added to a circuit in parallel
Which type of resistor allows us to easily adjust its resistance?
Variable resistor
A resistor which cannot vary the amount of resistance it provides is a…
Fixed resistor
In which type of resistor does the resistance vary with light intensity?
Light dependent resistor (LDR)
The resistance of a thermistor decreases when the temperature _______.
increases
Name the three wires that are normally present in UK plugs.
Live wire
Neutral wire
Earth wire
Wires are made of…
copper and coated in a layer of insulating plastic
Which wire prevents the electrical casing from becoming live?
Earth wire
Which wire supplies the current to the appliance?
live wire
Which wire completes the circuit, allowing current to flow?
Neutral wire
What is the voltage of the neutral wire?
0 V
Which two wires have the same voltage?
The earth wire and neutral wire are both at 0 V, whereas the live wire is at 230 V.
In a series circuit, the potential difference of the battery is…
…Shared across all of the components
Series circuits L
Series circuits only have a single loop.
Parallel circuits L
Parallel circuits have more than one loop.
In a series circuit, the current is
The same everywhere in the circuit
In a series circuit, the total resistance is ________ the sum of the individual resistances of each component.
equal to
Ohm’s law, which describes the relationship between voltage, current, and resistance is:
V=IR
In a series circuit, components with a greater resistance will always have a ________ share of the voltage.
greater
notes
The total current is shared between all of the parallel loops.
The sum of the current in each loop is equal to the total current.
