Scenario picker
Scenario
Your answer
Results
- Look at the six scenarios in the picker. Before you generate any values, predict which device you think will be the most efficient, and which will be the least. Write down your guesses.
- Pick the scenario you think is least efficient and press New values. Calculate the efficiency, type it in, and press Check. Were you right about the band it falls into?
- Add three different scenarios to the results table — one row each. Looking at your Wasted (J) column, which scenario wastes the most energy in absolute joules? Is it the same as the least efficient one? Explain why these two questions can give different answers.
- Generate three different sets of values for the same scenario (e.g. the kettle). The efficiency varies slightly each time. Why do you think real devices show this kind of variation?
- For your filament-lamp row, calculate what fraction of the input energy is wasted as heat and infrared. A modern LED bulb is around 40% efficient — roughly how many times brighter would it be than the filament lamp for the same energy supplied?
- A motor lifts a 5 kg load by 2 m using 200 J of electrical energy. Calculate the useful gravitational energy gained by the load (use g = 10 N/kg) and hence the motor's efficiency. Where might the missing energy have gone?
- Of the six scenarios, which one converts the highest fraction of input energy into the desired form, and which the lowest? Suggest a reason for the difference based on what you know about each device.