P5.1 - Alternating Current (Finished) Flashcards
How are alternating currents produced?
Alternating currents are produced by alternating voltages, where positive and negative ends keep alternating
What is the UK mains electricity supply supplying?
230V of ac current at 50Hz
What is the frequency of the UK ac mains supply?
50 Hz, 50 cycles per second
What is powered by direct current?
Anything that runs off a battery
What is the difference of AC and DC current?
Direct cureent always flows in the same direction, whereas AC current constantly is changing direction
Shat are the wires in a mains circuit?
A live wire - alternating,y positive and negative with every cycle
A neutral wire - at 0V
Where is the neutral mains wire earthed?
At the local electricity substation
Why is touching a live wire dangerous?
Your body is at 0V . This means that if you touch a live wire, a large potential difference is produced across your body and the current flows through you causing a large electric shock that could injure or kill
Why is even touching the live wire when a switch is off dangerous?
There is not current but there is still a large pd. Your body would provide a link between wire and earth so a current would flow through you
What is the national grid?
The national grid is a system of cables and transformers that covers the UK and connects power stations to consumers
Where does the national grid transfer electricity?
The national grid transfers electricity from power stations anywhere on it to wherever else where it is needed
How does the national grid cope to still meet demands with a power station failure or sudden increase in demand?
Power stations often run at well below their maximum power output so that there is spare capacity to cope with high demand. Lots of small power stations can also start up quickly and are kept on standby
How can power stations supply enough electricity needed without wasting too much due to varying demand?
They can predict when demand will be at it’s highest (e.g. mornings)
Why does the national grid transmit at a very high pd but low current?
A high current will cause wires to heat up, loosing lots of energy as thermal energy is transferred to the surroundings. So it’s more efficient to use a very high pd with a low current
What transformers are used where in the national grid?
Step up transformers are used by power stations to increase pd for transmission and step-down are used to bring it down to safe, usable levels for domestic use
