tps://www.ocr.org.uk/Images/705129-equation-sheet-physics-a.pdf","initialIndex":4,"initialQuestionWindow":[{"id":"1f637848-2e56-4037-9daa-86f61d5a4d0c","revisionId":"a4e53d16-03fc-4316-bc56-7fe2a510bed8","questionNumber":null,"questionType":"LA","specification":"An industrial spot welder uses a step-down transformer connected to the AC mains supply to deliver the extremely high currents needed to fuse sheet metal.\n\nThe table below shows the specifications and measurement data for this spot welder's transformer:\n\n| Parameter | Value |\n| :--- | :--- |\n| Number of turns on the primary coil | 800 |\n| Number of turns on the secondary coil | 5 |\n| Potential difference across the primary coil | 240 V |\n| Current in the secondary coil | 320 A |","difficulty":3,"difficultyBand":"medium","totalMarks":6,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"8dd31c14-b662-4b5a-a0f2-50df56d3df15","label":"a","content":"Calculate the potential difference across the secondary coil of this transformer.","markscheme":"- Recalls or uses the transformer equation $\\dfrac{V_s}{V_p} = \\dfrac{N_s}{N_p}$ or equivalent M1\n- Substitutes values into the equation: $V_s = 240 \\times \\dfrac{5}{800}$ M1\n- Calculates the secondary potential difference as $1.5\\text{ V}$ A1","marks":3,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"transformer_equation","label":"Use the transformer equation","steps":[{"type":"hyper_latex","block":{"nodes":[{"latex":"\\htmlData{anchor=ratio}{\\color{@red}{\\frac{V_s}{V_p}=\\frac{N_s}{N_p}}}"},{"text":"M1: use the transformer equation."},{"latex":"\\htmlData{anchor=substitute}{\\color{@red}{V_s}}=240\\times\\frac{5}{800}"},{"text":"M1: substitute the values."},{"latex":"\\htmlData{anchor=answer}{\\color{@green}{V_s=1.5\\ \\mathrm{V}}}"},{"text":"A1: correct secondary potential difference."}]},"order":1,"title":"Apply the turns ratio","description":"The 320 A secondary current is not needed here; use the 240 V primary potential difference, 800 primary turns and 5 secondary turns. Writing the transformer equation earns M1."}]}],"generatedAt":"2026-07-21T18:23:22.727Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]},{"id":"b28ced01-4e3e-4755-a357-1b23dad1f8b1","label":"b","content":"Calculate the current drawn by the primary coil from the mains supply, assuming the transformer operates at 100% efficiency.","markscheme":"- Recalls or uses power conservation $V_p I_p = V_s I_s$ or the inverse turns ratio relationship $I_p = I_s \\times \\dfrac{N_s}{N_p}$ M1\n- Substitutes the values into their chosen equation: $I_p = \\dfrac{1.5 \\times 320}{240}$ or $320 \\times \\dfrac{5}{800}$ M1\n- Calculates the primary current as $2.0\\text{ A}$ A1","marks":3,"order":1,"markingRubric":null,"explanation":{"methods":[{"id":"inverse_turns_ratio","label":"Use the inverse turns ratio","steps":[{"type":"text","order":0,"title":"Choose the current ratio","content":"For a transformer, the current ratio is the inverse of the turns ratio: fewer turns on the secondary coil means a larger secondary current. Using this relationship earns M1.","highlights":[{"text":"assuming the transformer operates at 100% efficiency","location":"specification"}]},{"type":"hyper_latex","block":{"nodes":[{"latex":"I_p=I_s\\times\\frac{N_s}{N_p}"},{"latex":"I_p=320\\times\\frac{5}{800}"}]},"order":1,"title":"Substitute the coil data","description":"Replace the secondary current with 320 A, the secondary turns with 5, and the primary turns with 800. This substitution earns the second M1."},{"type":"hyper_latex","block":{"nodes":[{"latex":"I_p=320\\times\\frac{5}{800}"},{"latex":"I_p=2.0\\ \\mathrm{A}"}]},"order":2,"title":"Calculate the primary current","description":"Now simplify the fraction and give the current with its unit. Calculating 2.0 A earns A1."}]},{"id":"conservation_of_power","label":"Use conservation of power","steps":[{"type":"hyper_latex","block":{"nodes":[{"latex":"\\frac{V_s}{240}=\\frac{5}{800}"}

Uses of magnetism

Question 4

Uses of magnetism Questions

Uses of magnetism

Question 4

Uses of magnetism Questions