es":[{"latex":"P_{\\mathrm{heating}}=I^2R"},{"latex":"I_{\\mathrm{shower}}\\text{ is large, so }\\htmlData{anchor=heating-risk}{I_{\\mathrm{shower}}^2R}\\text{ could be large}"},{"latex":"\\text{larger cross-sectional area}\\quad\\Longrightarrow\\quad\\htmlData{anchor=lower-resistance}{R\\text{ is lower}}"},{"latex":"R\\text{ lower}\\quad\\Longrightarrow\\quad P_{\\mathrm{heating}}\\text{ is reduced}"}],"highlights":[{"color":"red","style":"box","anchor":"heating-risk"},{"color":"sky","anchor":"lower-resistance"}]},"order":3,"title":"Prevent cable heating","description":"Electrical energy transferred by the cable’s resistance becomes thermal energy; P equals I squared R gives the rate of this heating. Reducing resistance is especially important when the current is large. A larger cross-sectional area gives lower resistance, reducing heating and helping prevent overheating, melted insulation or fire. This earns A1."}]}],"generatedAt":"2026-07-22T11:35:35.911Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"ad2a73a2-5d89-4f27-b374-5fe59fcd1852","revisionId":"a7061f15-3d49-41de-9f9c-dff9db8d4c82","questionNumber":null,"questionType":"LA","specification":"An industrial metal-cased workshop grinder is connected to a $230\\text{ V}$ mains electrical supply. Figure 1 shows a fault that has developed inside the grinder, where the live wire has come loose and is making direct contact with the metal outer casing.\n\n![Figure 1: Schematic showing a live wire fault in a metal-cased grinder.](https://assets.mathsgenie.co.uk/aqa-qb/8398a616-110c-4a99-b07a-b7c764a4386d.png)","difficulty":5,"difficultyBand":"medium","totalMarks":6,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"3fd047ac-9e57-4e60-85e8-cc529a2945d2","label":null,"content":"Explain how the combination of the earth wire and the fuse protects a workshop operator from receiving a fatal electric shock when this fault occurs.","markscheme":"- Identifies that the earth wire is connected directly to the metal casing of the grinder. B1\n- Explains that the earth wire has a very low electrical resistance. B1\n- Explains that when the live wire touches the metal casing, a low-resistance path is created from the live wire directly to the earth. M1\n- States that this low-resistance path causes a massive surge of current to flow through the live wire and the casing to the earth. M1\n- Explains that this large current passes through the fuse, causing the fuse wire to heat up, melt, and break the circuit. A1\n- Concludes that breaking the circuit isolates the grinder from the live supply, ensuring the casing is no longer live and preventing a fatal shock to the operator. A1","marks":6,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"earth_and_fuse","label":"Earth wire and fuse","steps":[{"type":"text","order":0,"title":"Identify the earth connection","content":"The earth wire is connected directly to the metal casing of the grinder. This earns the first B1.","highlights":[{"text":"metal-cased workshop grinder","location":"specification"}]},{"type":"text","order":1,"title":"Use low resistance","content":"The earth wire has a very low electrical resistance. This earns the second B1.","highlights":[{"text":"earth wire","location":"specification"}]},{"type":"text","order":2,"title":"Create the fault path","content":"When the loose live wire touches the casing, the casing and earth wire form a **low-resistance path** directly from the live wire to earth. This earns the M1: current has a route to earth rather than through the operator.","highlights":[{"text":"the live wire has come loose and is making direct contact with the metal outer casing","location":"specification"}]},{"type":"text","order":3,"title":"Explain the current surge","content":"Because this route has low resistance, a massive surge of current flows from the live wire, through the casing and earth wire, to ea

Mains electricity and safety

Question 6

Mains electricity and safety Questions

Mains electricity and safety

Question 6

Mains electricity and safety Questions