AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Exam Practice: The National Grid
The National Grid · Electricity · Lesson 8 of 10 · 14 marks · 15 minutes
|
Name |
|
Date |
|
Instructions
• Answer all the questions.
• Write your answers in the spaces provided.
• The marks for each question are shown in brackets - use this as a guide to how much to write.
• The answers are on separate pages at the back. Attempt every question before you look at them.
• Answer all questions. Use the mark allocation as a guide to how much to write.
Question 1 COMPLETE (2 marks)
Name the two types of transformer used in the National Grid and state what each does.
|
|
|
|
|
|
(Total for Question 1 = 2 marks)
Question 2 USE THE DIAGRAM (3 marks)
The diagram shows part of the National Grid. (a) Name the parts labelled A and B. (b) State why B is needed near homes.
|
|
|
|
|
|
|
|
(Total for Question 2 = 3 marks)
Question 3 EXPLAIN (3 marks)
Explain why using a high potential difference to transmit electricity is efficient.
|
|
|
|
|
|
|
|
(Total for Question 3 = 3 marks)
Question 4 CALCULATE (4 marks)
A power of 100 kW is transmitted at 10 000 V through cables of total resistance 2.0 Ω. Calculate the power wasted as heat in the cables.
|
|
|
|
|
|
|
|
|
|
|
|
(Total for Question 4 = 4 marks)
Question 5 EXPLAIN (2 marks)
The potential difference in the transmission cables is much higher than in homes. Explain why the potential difference in homes is reduced.
|
|
|
|
|
|
(Total for Question 5 = 2 marks)
TOTAL FOR PAPER = 14 MARKS
|
|
Answers and mark scheme
Check your answer only once you have written one.
Question 1 (2 marks)
Step-up transformers increase the potential difference; step-down transformers decrease the potential difference.
• Step-up increases pd 1 mark
• Step-down decreases pd 1 mark
Question 2 (3 marks)
(a) A is a step-up transformer; B is a step-down transformer. (b) To decrease the pd to a safe value for homes (230 V).
• A: step-up transformer 1 mark
• B: step-down transformer 1 mark
• Reduces the pd to a safe value for homes 1 mark
Question 3 (3 marks)
For the same power, a high potential difference means a smaller current. A smaller current causes less heating in the cables, so less energy is wasted.
• High pd means lower current for the same power 1 mark
• Lower current means less heating of the cables 1 mark
• So less energy wasted 1 mark
Question 4 (4 marks)
I = 100 000 ÷ 10 000 = 10 A; P = I²R = 10² × 2.0 = 200 W
• Rearranges to I = P ÷ V 1 mark
• 10 A 1 mark
• Correct substitution into I²R 1 mark
• 200 W 1 mark
Question 5 (2 marks)
230 V is safer for use in homes and works with appliances designed for it; a step-down transformer is used to decrease the pd.
• Safe for homes or appliances designed for 230 V 1 mark
• Step-down transformer decreases the pd 1 mark