ELECTRICITY Flashcards
Why is the current provided by a cell call direct current
Only flows in one direction
What is alternating current
Current that repeatedly reverses direction
What is the frequency and voltage of mains electricity
50Hz, 230V
What kind of current is supplied by mains electricity
Alternating current
What colours are the live, neutral and earth wires in a three core cable
Live - brown
Neutral - blue
Earth - green and yellow
What is the function of the live wire in a cable
Carries the alternating potential difference from the supply
What is the function of the neutral wire
Completes the circuit
What is the function of the earth wire
safety wire to stop the appliance becoming live
When is there current in the earth wire
When there’s a fault
Why is the live wire dangerous
Provides a large p.d that would cause a large current to flow through a person if they touched it
What is the national grid
nationwide network of cables and transformers that link power stations to customers
What are the step up transformers used for in the national grid
increase the p.d from the power station so that less current is needed to transfer the name amount of power so that less power is wasted due to heating
What two things does energy transfer to an appliance depend on
Power of appliance and time its switched on for
How does a material become charged
Gaining or losing electrons
What will two objects carrying the same type of charge do if they are brought close to each other
Repel each other
What happens to the strength of an electric field as. you get further from the charged object
It decreases
What is an electric current
Rate of flow of charge
What is the same at all points when charge flows in a closed loop
current
What must there be in a closed circuit so that electrical charge can flow
Potential difference
Which 2 factors does current depend on and what are their units
Resistance in ohms and p.d in volts
What happens to the current is the resistance is increased but the p.d stays the same
current decreases
what is an ohmic conductor
conductor where the current is directly proportional to the voltage so resistance is constant
what happens to the resistance of a filament lamp as its temperature increases
increases
what happens to the resistance of a thermistor as its temperature increases
decreases
what happens to the resistance of a light dependant resistor as its temperature increases
decreases
main features of a series circuit
- same current each component
- total p.d of power supply is shared between components
- total resistance of all components is the sum of the resistance of each component
main features of a parallel circuit
- pd across each branch is the same
- total current is the sum of currents in each branch
- total resistance of all resistors is less than the resistance of the smallest individual resistor
