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The National Grid

• National Grid = giant system of cables and transformers that covers UK and connects power stations to consumers, which are using electricity
• Transfers electrical power from power stations (supply) to anywhere on the grid where it is needed (demand)
• Electricity demand changes throughout the day = power stations must produce enough electricity to meet these demands
• Can predict when most electricity will be used: in the morning, coming home from school/work, when it starts to get dark/cold and popular TV events (sports)
• There is spare capacity for power stations to cope with the high demand as they work below their max power output
• Smaller stations can start up in case of emergencies
• To transmit huge amount of power = need either a high potential difference or a high current
• But with high current = lose lots of energy as wires heat up and energy is transferred to thermal energy store of surroundings
• Cheaper to increase the potential difference (400,000V) and keep current low as possible.
• Increasing potential difference = decreases current = decreases energy lost by heating the wires and surroundings = national grid efficient way of energy transfer.
• To get potential difference very high it requires transformers, big pylons with huge insulators
• Transformers step up the potential difference at one end for efficient transmission then bring it back down to a safe level at the other end .
• Potential difference is increased at STEP UP TRANSFORMER
• Potential difference is reduced at STEP DOWN TRANSFORMER

How long have you…? (present perfect 4) Exercises

Use the information given to create questions beginning with ‘How long…?’

• It is snowing.

• The weather is shining.

• John and Kate are married.

• My brother has gone on holiday.

• My aunty and uncle live in Canada.

• My sister is a teacher.

• I work at the chemist.

• I’ve known Susan since I was a baby.

• Jonathan is learning to speak to Mandarin.

Fill in the missing gaps in the sentences using the present perfect (=has/have + past participle)

• I have known Kate a long time.

• My brother has been playing the piano he was 11 years old.

• My mum and dad on holiday to America. They

gone since last Sunday.

• I Ben and Emma since primary school.

We to the same primary and secondary school.

• My sister learning to speak French because she
is going to France next month.

Use the appropriate words in the missing gaps.

have you lived       lives      to

has been       works        have known

I have bought       have worked.

• My sister in Spain. She is studying Spanish

with her friend Rosie. I Rosie since I was 5.

• Spencer like with Jamie. They have worked

together for 2 years.

• How long in Australia?

• a new dress for prom.

• He to Thorpe park.

Challenge: Create 4 of your own questions beginning with ‘How long……?’

1.

2.

3.

4.

1 2 3 4 5 6

“Every accomplishment starts
With the decision to try.” Gail Dever

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