Question 1: Define the term 'efficiency' in the context of energy transfers.

Answer: Efficiency is the ratio of useful energy transferred or converted to the total energy supplied, usually expressed as a percentage.

Question 2: Explain why no machine or device can be 100% efficient.

Answer: Because some energy is always lost as heat, sound, or other forms of energy due to friction and other inefficiencies.

Question 3: Calculate the efficiency of a machine that transfers 150 J of useful energy from a total input energy of 200 J. Use the formula: Efficiency = (Useful energy output / Total energy input) × 100%.

Answer: Efficiency = (150 / 200) × 100% = 75%

Question 4: A car engine converts 500 kJ of chemical energy into 350 kJ of kinetic energy. What is the efficiency of the engine?

Answer: Efficiency = (350 / 500) × 100% = 70%

Question 5: Describe one method to increase the efficiency of a household heating system.

Answer: Insulating the building to reduce heat loss, or using a more efficient boiler or heat pump.

Question 6: Identify two factors that cause energy transfer inefficiencies in electrical devices.

Answer: Friction within moving parts and heat loss due to resistance in electrical components.

Question 7: In an experiment, a student measures that a light bulb uses 60 J of electrical energy but only produces 10 J of light energy. Calculate its efficiency.

Answer: Efficiency = (10 / 60) × 100% ≈ 16.7%

Question 8: Propose one improvement to a wind turbine to increase its energy transfer efficiency.

Answer: Reducing mechanical friction in the moving parts or improving blade design to capture more wind energy.

Question 9: Explain how the concept of efficiency is applied in renewable energy technologies.

Answer: Efficiency in renewable energy technologies indicates how well these systems convert natural resources, such as sunlight, wind, or geothermal heat, into usable energy. High efficiency reduces waste and maximises energy output, making renewable sources more viable and sustainable for long-term energy needs.

Question 10: Identify and explain two practical precautions that should be taken during experiments measuring energy efficiency.

Answer: Ensure accurate measurements with calibrated instruments and avoid overheating or damage by not exceeding recommended power levels.