P4 - Supplying energy (PAPER 1) Flashcards
Why is the current provided by a cell called a direct current (d.c.)
only flows in one direction
What is an alternating current (a.c.)
current that repeatedly reverses direction
What kind of current is supplied by mains electricity
alternating current
What is the frequency and voltage of mains electricity
50 Hz, 230V
what colours are the live, neutral and earth wires in a three-core cable
live = brown
neutral = blue
earth = green
and yellow stripes
What is the function of the live wire in a three-core cable
carries the alternating potential difference from the supply
What is the function of the neutral wire in a three-core cable
completes the circuit
What is the function of the earth wire in a three-core cable
safety wire to stop the appliance becoming live
When is there a current in the earth wire
when there is 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 step-up transformers used for in the National Grid
increase the p.d. from the power station to the transmission cables
What are step-down transformers used for in the National Grid
decrease the p.d. from the transmission cables to the mains supply in buildings so that it is safe to use
How does having a large potential difference in the transmission cables help to make the National Grid an efficient way to transfer energy
large p.d. means a small current is needed to transfer the same amount of power, small current in the transmission cables means less electrical power is wasted due to heating
What two things does energy transfer to an appliance depend on
power of appliance, time it is switched on for
