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

Answer: Efficiency is a measure of how well energy is transferred or converted from one form to another, expressed as a percentage or ratio of useful energy output to total energy input.

Question 2: Explain why no energy transfer process is 100% efficient.

Answer: Because some energy is always lost as waste heat, sound, or other forms of non-useful energy due to inefficiencies in the system.

Question 3: Calculate the efficiency of a machine that uses 500 J of energy to perform useful work of 400 J.

Answer: Efficiency = (useful energy output / total energy input) × 100 = (400 J / 500 J) × 100 = 80%

Question 4: A car engine has an efficiency of 25%. If it receives 200 kJ of energy from fuel, how much useful work does it perform?

Answer: Useful work = (Efficiency / 100) × total energy = (25 / 100) × 200 kJ = 50 kJ

Question 5: List two practical ways to improve the efficiency of a household heating system.

Answer: Insulating the house to reduce heat loss and using a more efficient boiler or heater.

Question 6: Describe an experiment to measure the efficiency of a lamp converting electrical energy to light and heat.

Answer: Set up an electrical circuit with a lamp connected to a power supply and an ammeter and voltmeter to measure electrical energy input over a fixed time. Measure the light output using a light meter and estimate the heat produced. Calculate the efficiency by comparing useful light energy to electrical energy input, considering the heat loss.

Question 7: In industry, why is improving efficiency important for reducing energy costs and environmental impact?

Answer: Because higher efficiency means less energy waste, reducing costs and lowering the environmental impact by decreasing greenhouse gas emissions and resource consumption.

Question 8: Suggest safety precautions that should be considered when conducting practical experiments related to energy efficiency.

Answer: Ensure electrical equipment is properly insulated, avoid overloading circuits, and handle hot equipment with care to prevent burns.

Question 9: Identify the main sources of energy loss in a typical electric kettle.

Answer: Heat loss to the surroundings, heat escaping through the kettle’s material, and energy lost as sound during boiling.

Question 10: A wind turbine converts wind energy into electrical energy with an efficiency of 40%. If the wind provides 5000 kJ of energy in an hour, how much electrical energy is produced?

Answer: Electrical energy = 40% of 5000 kJ = 0.40 × 5000 kJ = 2000 kJ

Question 11: Explain in your own words how improving the insulation of a building affects its energy efficiency.

Answer: Better insulation reduces heat transfer out of the building, meaning less energy is needed to maintain a comfortable temperature, thus increasing overall efficiency.