MYP Physics · 05 · extended response
Choosing efficient classroom lighting
Work, energy and power · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 8
- Topics
- 2
- Answer
- Complete
A school will replace 100 classroom lamps. Both options provide the required brightness. Lamp A uses 12 W, transfers 9.0 W as useful light, and lasts 15 000 h. Lamp B uses 8.0 W, transfers 6.8 W as useful light, and lasts 10 000 h. Lamps operate for 5.0 h per school day on 180 days each year.
- a
Calculate Calculate the efficiency of each lamp.
2 marks - b
Determine Determine the annual electrical-energy saving if the school chooses B instead of A.
3 marks - c
Evaluate Recommend a lamp and explain what additional information could change the decision.
3 marks
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a
Calculate Calculate the efficiency of each lamp.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Calculates A: 9.0 ÷ 12 × 100% = 75%.
- 2
Calculates B: 6.8 ÷ 8.0 × 100% = 85%.
b
Determine Determine the annual electrical-energy saving if the school chooses B instead of A.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Finds total annual operating time per lamp = 5.0 × 180 = 900 h.
- 2
Finds power difference for 100 lamps = 100 × 4 W = 400 W = 0.400 kW.
- 3
Calculates saving = 0.400 × 900 = 360 kWh per year.
c
Evaluate Recommend a lamp and explain what additional information could change the decision.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Makes a recommendation supported by efficiency, annual energy, and/or service-life evidence.
- 2
Recognises the trade-off that B uses less energy but has a shorter stated life.
- 3
Identifies decision-relevant missing evidence such as purchase cost, light quality, repair access, embodied energy, or local electricity emissions.
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