# Understand the National Grid

In this worksheet, students will learn about the components that make up the national grid and the use of AC and DC electricity.

Key stage:  KS 4

GCSE Boards:   AQA, AQA Trilogy, AQA Synergy, OCR 21st Century, OCR Gateway, Pearson Edexcel

Difficulty level:

### QUESTION 1 of 10

There are sometimes some interesting rivalries in science. Newton and Hooke had a rivalry so strong that when Hooke died, Newton had all of Hooke’s his portraits burnt. Einstein had a rivalry with himself – basically discovering a branch of science called quantum mechanics and then spending his life trying to disprove it. But there are no greater rivalries than that of Nicola Tesla (the one the cars and named after) and Thomas Edison (the person who invented the lightbulb).

Tesla was born in Croatia and moved to America when he was young to try and earn some money. He was a painfully shy person, choosing to spend time in his room, not going out and only talking to people when it was necessary. Edison, however, was called the wizard of Maranello – an outgoing and brutal businessman who spent a lot of time showing off his inventions (including the lightbulb) in order to make more money.

Edison wanted to make electricity something that every American in could enjoy – for a price that would make him the richest person in the world. There was one problem with the plan – using his DC electricity he couldn’t transport his electricity very far before it all leaked out of the wires.

Frustrated with this, Edison issued a challenge to the young Tesla who he had employed based on his reputation. He said ‘If you find a way of transporting electricity more effectively, I’ll pay you \$50,000’ which is about \$10 million now. Tesla, obviously impressed with this amount and the challenge, worked day and night for months and came up with a solution – he called it AC. Edison took this idea and when Tesla asked to be paid, Edison laughed at him and said ‘You don’t understand American humour, I was never going to pay you’.

Tesla quit working for Edison and moved to work with Westinghouse where it was his aim to make electricity free for everyone. Edison didn’t like this and started a smear campaign, electrocuting elephants and people using Tesla’s AC as a way of showing how dangerous it was (but DC was actually more dangerous). But what is the difference between AC and DC I hear you cry? Let's take a look at them.

(INSET IMAGE OF AC AND DC HERE).

Things to remember:

1 - in AC the electrons move from side to side (shown by the up and down motion in the graph). This is done at about 50 times every second (50Hz) in the UK. AC is safer and wastes less energy than DC.

2 - IN DC all of the electron flow around the circuit like you would expect them to. This is the type of electricity you get in batteries, and it is really useful for things like phones and computers. They almost always need a DC supply and so most of them have to convert the AC they get from the plug into DC.

However, the benefits of AC won out in the end and Edison started using it to distribute his electricity as well. This made Edison the richest man in the world at the time and Tesla died with hardly any money.

What does this have to do with the National Gird? Well, we still use Teslas AC in our national grid today – let’s take a look at it.

The important parts to remember in this image are:

1 - Those black boxes are called transformers, and they change the voltage up and down. A high voltage will make it very efficient to send the electricity a long way, but it needs to be moved back down so it can be sued by your house.

2 - The voltage in the 'high tension' wires is about 400,000 V and in your homes, it is about 230 V.

3 - This ONLY works with AC, not DC. This is why Tesla's idea was better!

In the modern national grind system, do we use AC or DC?

AC

DC

Do batteries use AC or DC power?

AC

DC

From the list below, chose the correct value for mains voltage in the UK and the frequency of the power supply in the UK.

What is the function of a transformer?

Change the voltage

Change the current

A robot in disguise

Change the resistence

## Column B

1
Step-up transformer
2
Home
3
Step-down transformer
4
High tension wires
5
Genroator

Power is lost in the transfer of electricity along wires. Complete the sentence "The energy is lost as..."

Describe the function of a step-down transformer (2 marks).

Describe the function of the national grid (1 mark).

Compare AC and DC in terms of movement of electrons (2 marks).

Describe what happens to the electricity when it goes through a step-up transformer (2 marks).

• Question 1

In the modern national grind system, do we use AC or DC?

AC
EDDIE SAYS
AC is used in the modern national grid - only AC is able to work with the transformers that are needed in the national grid to transmit electricity effectively over a long distance without losing a huge amount.
• Question 2

Do batteries use AC or DC power?

DC
EDDIE SAYS
Batteries are a store of DC power - they provide a constant flow of electrons to the circuit instead of moving them backwards and forwards. This is much better for electrical circuits but means that the power cannot be transmitted over long distances. That's why you will find remote controls and stuff powered by batteries and not by the mains.
• Question 3

From the list below, chose the correct value for mains voltage in the UK and the frequency of the power supply in the UK.

EDDIE SAYS
This is a case of just trying to remember the facts, but if we are being totally honest there are much more important things for you to remember. The most this will ever get you are 2 marks, but something like remembering the circuit symbols could get you a lot more marks. All we're saying is be intelligent about what you put your time and effort into.
• Question 4

What is the function of a transformer?

Change the voltage
Change the current
EDDIE SAYS
A transformer needs to change BOTH the voltage and the current of the electricity that is passing thought it. It needs a low current so it wastes as little energy as possible when it is going through the wires. It achieves this by having a really high voltage so most of the energy can stay in the wires. Long and short, high voltage and low current are the keys to a bright home.
• Question 5

## Column B

1
Genroator
2
Step-up transformer
3
High tension wires
4
Step-down transformer
5
Home
EDDIE SAYS
So, the pattern goes like this: 1 - You need to make (generate) the electricity, so we need to start off with a generator. 2 - You need the voltage to be as high as possible when transmitting the electricity, it needs to be stepped up. This means you need a step-up transformer. 3 - You need to move the electricity through cables - these are held at a high voltage, so they are High tension cables. 4 - You need the voltage to be brought back down to 230 V before it goes into the house, so you will need another step-down transformer to put it back to normal 230 V. 5 - Your house needs the electricity - so you need to put your house in there at the end...
• Question 6

Power is lost in the transfer of electricity along wires. Complete the sentence "The energy is lost as..."

Heat
EDDIE SAYS
You will learn more about why it is heat when you do the module on electricity. Essentially, the electrons bash into stuff in the wire that is not moving. This causes that stuff to vibrate, and we all know that vibrating particles are hot particles. The more they vibrate, the more heat they have. Heat is energy loss and we want to stop that as much as possible :)
• Question 7

Describe the function of a step-down transformer (2 marks).

EDDIE SAYS
Remember, if it is worth 2 marks then you need to write 2 things. In this case, we wanted you to state that the voltage AND current change in a transformer. Did you stop that we said step-down transformer in the question? This is because we needed you to specifically talk about what happens to BOTH the voltage and the current in a STEP-DOWN transformer. Read the question and be specific: Step-down = voltage goes down = current goes up.
• Question 8

Describe the function of the national grid (1 mark).

EDDIE SAYS
Just like in all subjects words are important in science. You must use the term 'Transfer' and 'generate' to be able to accurately describe what the national grid does. It Transfers the energy from where it is Generated to where it is needed.
• Question 9

Compare AC and DC in terms of movement of electrons (2 marks).

EDDIE SAYS
When we write compare, what we really mean is we want you to state something about each of these things and then say how they are different. In this example, all you need to do is say how the electrons move in AC and DC - that is enough of a comparison. AC - side to side DC - constantly moving in one direction.
• Question 10

Describe what happens to the electricity when it goes through a step-up transformer (2 marks).

EDDIE SAYS
Aha! Did you remember which way round the step-up and step-down transformers go? Did you spot it int he question? Step-up = voltage up = current down. The direction of the transformer always talks about the voltage.