GCSE Physics Exam Doctor

Download GCSE Physics Exam Doctor

Post on 07-Jan-2016

39 views

Category:

Documents

0 download

Embed Size (px)

DESCRIPTION

GCSE Physics Exam Doctor. Mains Electricity. Question 2. Question 3. Question 4. Question 1. Question 5. GCSE Physics Exam Doctor. Mains Electricity. Question 1. - PowerPoint PPT Presentation

TRANSCRIPT

<ul><li><p>GCSE Physics Exam DoctorMains ElectricityQuestion1Question2Question3Question4Question5</p></li><li><p>GCSE Physics Exam DoctorMains ElectricityQuestion 1</p></li><li><p> The diagram shows the wiring inside a plug fitted to a washing machine, though two of the wires are not their correct colours. a) i) What two errors have been made in wiring the plug? (2 marks)ii) Complete the label. (1 mark) </p></li><li><p> iii) What should be the colour of the live wire? (1 mark) b) i) Which part of the washing machine should the earth be connected to ? (1 mark) ii) What is the purpose of the fuse? (1 mark)</p></li><li><p>If the case becomes live, a large current passes to ., causing the . to melt. This breaks the .. connection to the mains supply. The fuse and .wire together therefore protect the user from electric shock.earth fuse live neutral plug iii) Complete the sentences using the words from the box. Each word may be used once, more than once, or not at all. (4 marks)</p></li><li><p> The diagram shows the wiring inside a plug fitted to a washing machine, though two of the wires are not their correct colours. a) i) What two errors have been made in wiring the plug? (2 marks)ii) Complete the label. (1 mark) The wire to the fuse is all fuzzy. The earth wire is bulging. The outer insulation is too far down. neutral wire</p></li><li><p> iii) What should be the colour of the live wire? (1 mark) b) i) Which part of the washing machine should the earth be connected to ? (1 mark) ii) What is the purpose of the fuse? (1 mark)The live wire should be blueTo the green and yellow bitTo limit the current to a safe value.</p></li><li><p>If the case becomes live, a large current passes to ., causing the . to melt. This breaks the .. connection to the mains supply. The fuse and .wire together therefore protect the user from electric shock.earth fuse live neutral plug iii) Complete the sentences using the words from the box. Each word may be used once, more than once, or not at all. (4 marks)the plugfuseearthlive</p></li><li><p> The diagram shows the wiring inside a plug fitted to a washing machine, though two of the wires are not their correct colours. a) i) What two errors have been made in wiring the plug? (2 marks)ii) Complete the label. (1 mark) Mark schemeAll the bits of the wire, by the fuse, should be inside the insulation.The cord insulation exposing the inner, coloured insulation. neutral wire</p></li><li><p> iii) What should be the colour of the live wire? (1 mark) b) i) Which part of the washing machine should the earth be connected to ? (1 mark) ii) What is the purpose of the fuse? (1 mark)Mark schemeThe live wire is brown.It should be connected to the outer casing of the washing machine.Cutting off the current if it gets too big.</p></li><li><p>If the case becomes live, a large current passes to ., causing the . to melt. This breaks the .. connection to the mains supply. The fuse and .wire together therefore protect the user from electric shock.earth fuse live neutral plug iii) Complete the sentences using the words from the box. Each word may be used once, more than once, or not at all. (4 marks)Mark schemeearthfuseliveearth</p></li><li><p> The diagram shows the wiring inside a plug fitted to a washing machine, though two of the wires are not their correct colours. a) i) What two errors have been made in wiring the plug? (2 marks)ii) Complete the label. (1 mark) The wire to the fuse is all fuzzy. The earth wire is bulging. The outer insulation is too far down. neutral wireAlthough this is badly expressed, it is just sufficient to score, as the idea is there that all the bits of the wire should be inside the insulation.The bulging earth wire is irrelevant, the score is for the cord insulation exposing the inner, coloured insulation.33</p></li><li><p> iii) What should be the colour of the live wire? (1 mark) b) i) Which part of the washing machine should the earth be connected to ? (1 mark) ii) What is the purpose of the fuse? (1 mark)The live wire should be blueTo the green and yellow bitTo limit the current to a safe value.The live wire is brown, the neutral blue.The question has been misunderstood. The earth wire is the green and yellow one, it should be connected to the outer casing of the washing machine.Although this looks alright at first sight, it implies that the current reaches a limit and is not allowed to increase anymore, but still flows. An answer including cutting off the current if it gets too big is required.03</p></li><li><p>If the case becomes live, a large current passes to ., causing the . to melt. This breaks the .. connection to the mains supply. The fuse and .wire together therefore protect the user from electric shock.earth fuse live neutral plug iii) Complete the sentences using the words from the box. Each word may be used once, more than once, or not at all. (4 marks)the plugfuseearthliveA large current passes to earth, causing the fuse to melt. This breaks the live connection to the mains supply. The fuse and earth wire together therefore protect the user from electric shock. The function of the earth wire is commonly misunderstood. In free-response questions a reply about the current going through the earth wire instead of through you is common. The earth wire would be ineffective without the fuse.14</p></li><li><p>GCSE Physics Exam DoctorMains ElectricityQuestion 2</p></li><li><p>a) A current of 0.02 A could give a serious electrical shock to a person. If the resistance of a body is 10 000 ohms, calculate the voltage which will cause this current. (3 marks)b) Explain why it is dangerous to operate a light switch with a wet hand. (2 marks)Some appliances have an earth wire fitted to them to prevent the user receiving an electric shock. i) What is the colour code for the earth wire in a plug? (1 mark)</p></li><li><p>ii) Appliances with a plastic casing do not have an earth connection. Explain why this connection is not needed. (2 marks)d) i) Explain how the earth wire prevents a person receiving an electric shock when the live wire comes into contact with the metal casing of an appliance. (2 marks)d) ii) Why must the resistance of the earth wire to an appliance be very low? (2 marks)</p></li><li><p>a) A current of 0.02 A could give a serious electrical shock to a person. If the resistance of a body is 10 000 ohms, calculate the voltage which will cause this current. (3 marks)b) Explain why it is dangerous to operate a light switch with a wet hand. (2 marks)Some appliances have an earth wire fitted to them to prevent the user receiving an electric shock. i) What is the colour code for the earth wire in a plug? (1 mark)V = I x R V = 0.02 x 10 000 = 200Water conducts electricity and magnifies the shockGreen and yellow</p></li><li><p>ii) Appliances with a plastic casing do not have an earth connection. Explain why this connection is not needed. (2 marks)d) i) Explain how the earth wire prevents a person receiving an electric shock when the live wire comes into contact with the metal casing of an appliance. (2 marks)d) ii) Why must the resistance of the earth wire to an appliance be very low? (2 marks)You cant get a shock from plastic. It insulates the current.The earth wire is a safety device it prevents a shock. The live wire conducts to the casing and causes a shock if you touch it. With an earth wire the current goes to the earth instead of through you.So that all of the current can go down that route instead of through you.</p></li><li><p>a) A current of 0.02 A could give a serious electrical shock to a person. If the resistance of a body is 10 000 ohms, calculate the voltage which will cause this current. (3 marks)b) Explain why it is dangerous to operate a light switch with a wet hand. (2 marks)Some appliances have an earth wire fitted to them to prevent the user receiving an electric shock. i) What is the colour code for the earth wire in a plug? (1 mark)Mark schemeV = I x R V = 0.02 x 10 000 = 200VImpure water conducts electricity and this may lead to a current in the body.Green and yellow</p></li><li><p>ii) Appliances with a plastic casing do not have an earth connection. Explain why this connection is not needed. (2 marks)d) i) Explain how the earth wire prevents a person receiving an electric shock when the live wire comes into contact with the metal casing of an appliance. (2 marks)d) ii) Why must the resistance of the earth wire to an appliance be very low? (2 marks)Mark schemePlastic is an insulator, there is no possibility of a current, the casing cannot become live.The low resistance path to earth allows a large current to flow through the earth wire, which blows the fuse.The resistance must be low, so that there can be a large current that will blow the fuse.</p></li><li><p>a) A current of 0.02 A could give a serious electrical shock to a person. If the resistance of a body is 10 000 ohms, calculate the voltage which will cause this current. (3 marks)b) Explain why it is dangerous to operate a light switch with a wet hand. (2 marks)Some appliances have an earth wire fitted to them to prevent the user receiving an electric shock. i) What is the colour code for the earth wire in a plug? (1 mark)V = I x R V = 0.02 x 10 000 = 200Water conducts electricity and magnifies the shockGreen and yellowScores 1 for using V = I x RScores 1 for arriving at 200, but has omitted the unit VScores 1 for water conducts, though, in fact, pure water does not conduct, only impur...</p></li></ul>