iciency/questions","formulaUrl":"https://www.ocr.org.uk/Images/705129-equation-sheet-physics-a.pdf","initialIndex":23,"initialQuestionWindow":[{"id":"7af40f40-f5ff-4f52-b78b-6cfb834b3a26","revisionId":"74848066-fc5e-4e95-bcef-bba34ad8fbb7","questionNumber":null,"questionType":"LA","specification":"The table compares a halogen lamp and an LED lamp which produce the same intensity of light.\n\n| | Halogen lamp | LED lamp |\n| :--- | :---: | :---: |\n| **Power** | 40 W | 0.008 kW |\n| **Lifetime** | 3000 hours | 24,000 hours |\n| **Cost to buy** | £2.00 | £6.00 |\n| **Cost to run over 1 year** | £15.00 | £3.00 |\n| **Dimmable** | Yes | No |\n| **Structure** | Glass | Plastic |","difficulty":3,"difficultyBand":"medium","totalMarks":14,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"226cacf9-b821-4063-b49f-cacbc8866431","label":"a","content":"State the power of the halogen lamp in kW.","markscheme":"- Converts $40\\text{ W}$ to $\\text{kW}$ by dividing by $1000$ to get $0.04\\text{ kW}$ B1","marks":1,"order":0,"markingRubric":null,"explanation":null,"options":[]},{"id":"90c62dd0-03b3-4808-9417-7311954d812e","label":"b","content":"Calculate the energy transferred by the LED lamp during its lifetime. Use the equation:\n\\[\\text{energy transferred} = \\text{power} \\times \\text{time}\\]\nGive your answer in kWh.","markscheme":"- Recalls or uses $\\text{energy} = \\text{power} \\times \\text{time} = 0.008\\text{ kW} \\times 24{,}000\\text{ hours}$ M1\n- Calculates energy transferred as $192\\text{ kWh}$ A1","marks":2,"order":1,"markingRubric":null,"explanation":null,"options":[]},{"id":"344a99d8-60b7-4682-82eb-5fe342fed7d0","label":"c","content":"In 1 year, the halogen lamp transfers 75 kWh of energy. This costs £15.00. What is the cost of 1 kWh of electricity?","markscheme":"- Divides total cost by energy used: $\\frac{£15.00}{75\\text{ kWh}}$ M1\n- Calculates cost per kWh as $£0.20$ (or $20\\text{p}$) A1","marks":2,"order":2,"markingRubric":null,"explanation":null,"options":[]},{"id":"f8948dad-5338-438d-bbff-907cb1a80795","label":"d","content":"Calculate the number of halogen lamps a person must buy during the lifetime of one LED lamp.","markscheme":"- Divides lifetime of LED by lifetime of halogen: $\\frac{24{,}000}{3{,}000}$ M1\n- Calculates the number of lamps as $8$ A1","marks":2,"order":3,"markingRubric":null,"explanation":null,"options":[]},{"id":"1d031279-666b-42d8-a680-366d99b319da","label":"e","content":"Suggest one reason for and one reason against using LED lamps, using the data in the table.","markscheme":"- States one valid reason for LED lamps from the table (e.g. lower running costs or longer lifetime) B1\n- States one valid reason against LED lamps from the table (e.g. higher initial cost or non-dimmable) B1","marks":2,"order":4,"markingRubric":null,"explanation":null,"options":[]},{"id":"6c48b4a0-f5fe-438e-9f88-cb207dccdf39","label":"f","content":"One LED lamp has an efficiency of 0.35. In one second, the input energy transferred by the lamp is 20 J. Calculate the energy wasted by the lamp in one second. Use the equation:\n\\[\\text{efficiency} = \\frac{\\text{useful output energy transfer}}{\\text{input energy transfer}}\\]","markscheme":"- Calculates useful output energy: $0.35 \\times 20\\text{ J} = 7\\text{ J}$ (or determines wasted fraction as $1 - 0.35 = 0.65$) M1\n- Calculates wasted energy as $20\\text{ J} - 7\\text{ J} = 13\\text{ J}$ (or $0.65 \\times 20\\text{ J} = 13\\text{ J}$) A1","marks":2,"order":5,"markingRubric":null,"explanation":null,"options":[]},{"id":"0c4dccda-e55d-4aa2-ab15-837a0afa1ef3","label":"g","content":"The graph shows how the total cost of buying and using each lamp varies with the number of days each lamp is used.\n\n![A graph showing Total Cost in pounds (#) on the vertical y-axis, from #0 to #14 with major grid lines every #2 and minor grid lines every #0.20. The horizontal x-axis shows the Number

Power and efficiency

Question 13

Power and efficiency Questions

Power and efficiency

Question 13

Power and efficiency Questions