Year 9 Science • AC9S9U05 • Authored homework
Conservation of Energy & Efficiency
Apply conservation of energy to analyse systems, identify useful and wasted energy transfers, and calculate or explain efficiency in real contexts.
Part A
Short-answer questions
State the law of conservation of energy.
What is meant by a useful energy output?
What is meant by wasted or dissipated energy?
Write the efficiency formula in words or symbols.
A lamp receives 100 J of electrical energy and produces 25 J of light. Calculate its efficiency.
Why does a device usually warm up when it operates?
Explain why energy is not destroyed when a moving object slows down.
Give one example of an energy store and one example of an energy transfer pathway.
What information is shown in a Sankey diagram?
Correct this misconception: “A 40% efficient device loses 60% of its energy forever.”
Part B
Long-answer questions
Trace the energy changes in a phone while it is charging and then being used. Identify useful and dissipated transfers.
A motor receives 500 J of electrical energy and outputs 320 J as kinetic energy. Calculate efficiency and explain where the rest of the energy goes.
Draw or describe a Sankey diagram for a toaster, including useful heating and energy transferred to surroundings.
Explain why an electric car, bicycle or fan cannot be 100% efficient in practice.
Compare the energy efficiency of an incandescent globe and an LED globe using useful and wasted energy.
Use conservation of energy to explain a roller-coaster car moving from a high point to a low point with friction.
A student says, “The best device is always the one with the highest efficiency.” Evaluate this claim using at least two other factors.
Create an energy account for a bouncing ball, explaining why it does not return to the original height.
Explain how insulation improves the useful energy outcome in a home, fridge or drink bottle.
Write a full response analysing one appliance or vehicle using input energy, useful output, dissipated energy and efficiency.
Part C
Research and understanding task
Research the efficiency of one real device, such as an LED bulb, solar panel, petrol engine, electric motor, kettle or refrigerator. Explain the input energy, useful output, wasted transfers and one design feature that improves efficiency.